diff --git a/examples/COUPLE/plugin/liblammpsplugin.c b/examples/COUPLE/plugin/liblammpsplugin.c
index 5228e07e9c..011c320254 100644
--- a/examples/COUPLE/plugin/liblammpsplugin.c
+++ b/examples/COUPLE/plugin/liblammpsplugin.c
@@ -110,6 +110,8 @@ liblammpsplugin_t *liblammpsplugin_load(const char *lib)
   ADDSYM(extract_variable);
   ADDSYM(extract_variable_datatype);
   ADDSYM(set_variable);
+  ADDSYM(set_string_variable);
+  ADDSYM(set_internal_variable);
   ADDSYM(variable_info);
 
   ADDSYM(gather_atoms);
diff --git a/examples/COUPLE/plugin/liblammpsplugin.h b/examples/COUPLE/plugin/liblammpsplugin.h
index 92398dfb27..1d647e8e93 100644
--- a/examples/COUPLE/plugin/liblammpsplugin.h
+++ b/examples/COUPLE/plugin/liblammpsplugin.h
@@ -152,9 +152,11 @@ struct _liblammpsplugin {
 
   void *(*extract_compute)(void *, const char *, int, int);
   void *(*extract_fix)(void *, const char *, int, int, int, int);
-  void *(*extract_variable)(void *, const char *, char *);
+  void *(*extract_variable)(void *, const char *, const char *);
   int (*extract_variable_datatype)(void *, const char *);
-  int (*set_variable)(void *, char *, char *);
+  int (*set_variable)(void *, const char *, const char *);
+  int (*set_string_variable)(void *, const char *, const char *);
+  int (*set_internal_variable)(void *, const char *, double);
   int (*variable_info)(void *, int, char *, int);
 
   void (*gather_atoms)(void *, const char *, int, int, void *);
diff --git a/fortran/lammps.f90 b/fortran/lammps.f90
index 28e40bca44..071dffebc0 100644
--- a/fortran/lammps.f90
+++ b/fortran/lammps.f90
@@ -118,6 +118,8 @@ MODULE LIBLAMMPS
     PROCEDURE :: extract_fix            => lmp_extract_fix
     PROCEDURE :: extract_variable       => lmp_extract_variable
     PROCEDURE :: set_variable           => lmp_set_variable
+    PROCEDURE :: set_string_variable    => lmp_set_string_variable
+    PROCEDURE :: set_internal_variable  => lmp_set_internal_variable
     PROCEDURE, PRIVATE :: lmp_gather_atoms_int
     PROCEDURE, PRIVATE :: lmp_gather_atoms_double
     GENERIC   :: gather_atoms           => lmp_gather_atoms_int, &
@@ -557,6 +559,21 @@ MODULE LIBLAMMPS
       INTEGER(c_int) :: lammps_set_variable
     END FUNCTION lammps_set_variable
 
+    FUNCTION lammps_set_string_variable(handle, name, str) BIND(C)
+      IMPORT :: c_int, c_ptr
+      IMPLICIT NONE
+      TYPE(c_ptr), VALUE :: handle, name, str
+      INTEGER(c_int) :: lammps_set_string_variable
+    END FUNCTION lammps_set_string_variable
+
+    FUNCTION lammps_set_internal_variable(handle, name, val) BIND(C)
+      IMPORT :: c_int, c_ptr, c_double
+      IMPLICIT NONE
+      TYPE(c_ptr), VALUE :: handle, name
+      REAL(c_double), VALUE :: val
+      INTEGER(c_int) :: lammps_set_internal_variable
+    END FUNCTION lammps_set_internal_variable
+
     SUBROUTINE lammps_gather_atoms(handle, name, type, count, data) BIND(C)
       IMPORT :: c_int, c_ptr
       IMPLICIT NONE
@@ -1631,6 +1648,43 @@ CONTAINS
     END IF
   END SUBROUTINE lmp_set_variable
 
+  ! equivalent function to lammps_set_string_variable
+  SUBROUTINE lmp_set_string_variable(self, name, str)
+    CLASS(lammps), INTENT(IN) :: self
+    CHARACTER(LEN=*), INTENT(IN) :: name, str
+    INTEGER :: err
+    TYPE(c_ptr) :: Cstr, Cname
+
+    Cstr = f2c_string(str)
+    Cname = f2c_string(name)
+    err = lammps_set_string_variable(self%handle, Cname, Cstr)
+    CALL lammps_free(Cname)
+    CALL lammps_free(Cstr)
+    IF (err /= 0) THEN
+      CALL lmp_error(self, LMP_ERROR_WARNING + LMP_ERROR_WORLD, &
+        'WARNING: unable to set string variable "' // name &
+        // '" [Fortran/set_variable]')
+    END IF
+  END SUBROUTINE lmp_set_string_variable
+
+  ! equivalent function to lammps_set_internal_variable
+  SUBROUTINE lmp_set_internal_variable(self, name, val)
+    CLASS(lammps), INTENT(IN) :: self
+    CHARACTER(LEN=*), INTENT(IN) :: name
+    REAL(KIND=c_double), INTENT(IN) :: val
+    INTEGER :: err
+    TYPE(c_ptr) :: Cstr, Cname
+
+    Cname = f2c_string(name)
+    err = lammps_set_internal_variable(self%handle, Cname, val)
+    CALL lammps_free(Cname)
+    IF (err /= 0) THEN
+      CALL lmp_error(self, LMP_ERROR_WARNING + LMP_ERROR_WORLD, &
+        'WARNING: unable to set internal variable "' // name &
+        // '" [Fortran/set_variable]')
+    END IF
+  END SUBROUTINE lmp_set_internal_variable
+
   ! equivalent function to lammps_gather_atoms (for integers)
   SUBROUTINE lmp_gather_atoms_int(self, name, count, data)
     CLASS(lammps), INTENT(IN) :: self
diff --git a/python/lammps/core.py b/python/lammps/core.py
index 1ff123760b..f4ba7d398b 100644
--- a/python/lammps/core.py
+++ b/python/lammps/core.py
@@ -282,6 +282,8 @@ class lammps(object):
     self.lib.lammps_config_accelerator.argtypes = [c_char_p, c_char_p, c_char_p]
 
     self.lib.lammps_set_variable.argtypes = [c_void_p, c_char_p, c_char_p]
+    self.lib.lammps_set_string_variable.argtypes = [c_void_p, c_char_p, c_char_p]
+    self.lib.lammps_set_internal_variable.argtypes = [c_void_p, c_char_p, c_double]
 
     self.lib.lammps_has_style.argtypes = [c_void_p, c_char_p, c_char_p]
 
@@ -1252,6 +1254,8 @@ class lammps(object):
   def set_variable(self,name,value):
     """Set a new value for a LAMMPS string style variable
 
+    .. deprecated:: TBD
+
     This is a wrapper around the :cpp:func:`lammps_set_variable`
     function of the C-library interface.
 
@@ -1271,6 +1275,52 @@ class lammps(object):
 
   # -------------------------------------------------------------------------
 
+  def set_string_variable(self,name,value):
+    """Set a new value for a LAMMPS string style variable
+
+    .. versionadded:: TBD
+
+    This is a wrapper around the :cpp:func:`lammps_set_string_variable`
+    function of the C-library interface.
+
+    :param name: name of the variable
+    :type name: string
+    :param value: new variable value
+    :type value: any. will be converted to a string
+    :return: either 0 on success or -1 on failure
+    :rtype: int
+    """
+    if name: name = name.encode()
+    else: return -1
+    if value: value = str(value).encode()
+    else: return -1
+    with ExceptionCheck(self):
+      return self.lib.lammps_set_string_variable(self.lmp,name,value)
+
+  # -------------------------------------------------------------------------
+
+  def set_internal_variable(self,name,value):
+    """Set a new value for a LAMMPS internal style variable
+
+    .. versionadded:: TBD
+
+    This is a wrapper around the :cpp:func:`lammps_set_internal_variable`
+    function of the C-library interface.
+
+    :param name: name of the variable
+    :type name: string
+    :param value: new variable value
+    :type value: float or compatible. will be converted to float
+    :return: either 0 on success or -1 on failure
+    :rtype: int
+    """
+    if name: name = name.encode()
+    else: return -1
+    with ExceptionCheck(self):
+      return self.lib.lammps_set_internal_variable(self.lmp,name,value)
+
+  # -------------------------------------------------------------------------
+
   # return vector of atom properties gathered across procs
   # 3 variants to match src/library.cpp
   # name = atom property recognized by LAMMPS in atom->extract()
diff --git a/src/library.cpp b/src/library.cpp
index a629df7b8c..706e016888 100644
--- a/src/library.cpp
+++ b/src/library.cpp
@@ -2451,19 +2451,59 @@ int lammps_extract_variable_datatype(void *handle, const char *name)
 }
 
 /* ---------------------------------------------------------------------- */
+// for printing obsolete function call warning only once
+static int set_variable_deprecated_flag = 1;
 
 /** Set the value of a string-style variable.
- *
- * This function assigns a new value from the string str to the
- * string-style variable name. Returns -1 if a variable of that
- * name does not exist or is not a string-style variable, otherwise 0.
- *
+\verbatim embed:rst
+
+.. deprecated:: TBD
+
+This function assigns a new value from the string str to the
+string-style variable *name*. Returns -1 if a variable of that
+name does not exist or is not a string-style variable, otherwise 0.
+
+.. warning::
+
+   This function is deprecated and :cpp:func:`lammps_set_string_variable`
+   should be used instead.
+
+   \endverbatim
+
+* \param  handle  pointer to a previously created LAMMPS instance
+ * \param  name    name of the variable
+ * \param  str     new value of the variable
+ * \return         0 on success or -1 on failure */
+
+int lammps_set_variable(void *handle, const char *name, const char *str)
+{
+  if (set_variable_deprecated_flag) {
+    fprintf(stderr,"Using the 'lammps_set_variable()' function is deprecated. "
+            "Please use 'lammps_set_string_variable()' instead.\n");
+    set_variable_deprecated_flag = 0;
+  }
+  return lammps_set_string_variable(handle, name, str);
+}
+
+/* ---------------------------------------------------------------------- */
+
+/** Set the value of a string-style variable.
+\verbatim embed:rst
+
+.. versionadded:: TBD
+
+This function assigns a new value from the string str to the
+string-style variable *name*.  Returns -1 if a variable of that
+name does not exist or is not a string-style variable, otherwise 0.
+
+\endverbatim
+
  * \param  handle  pointer to a previously created LAMMPS instance
  * \param  name    name of the variable
  * \param  str     new value of the variable
  * \return         0 on success or -1 on failure
  */
-int lammps_set_variable(void *handle, char *name, char *str)
+int lammps_set_string_variable(void *handle, const char *name, const char *str)
 {
   auto lmp = (LAMMPS *) handle;
   int err = -1;
@@ -2477,6 +2517,35 @@ int lammps_set_variable(void *handle, char *name, char *str)
   return err;
 }
 
+/* ---------------------------------------------------------------------- */
+
+/** Set the value of an internal-style variable.
+ *
+ * This function assigns a new value value to an internal-style variable.
+ * Returns -1 if a variable of that name does not exist or is not an
+ * internal-style variable, otherwise 0.
+ *
+ * \param  handle  pointer to a previously created LAMMPS instance
+ * \param  name    name of the variable
+ * \param  value   new value of the variable
+ * \return         0 on success or -1 on failure
+ */
+int lammps_set_internal_variable(void *handle, const char *name, double value)
+{
+  auto lmp = (LAMMPS *) handle;
+
+  BEGIN_CAPTURE
+  {
+    int ivar = lmp->input->variable->find(name);
+    if (ivar < 0) return -1;
+    if (lmp->input->variable->internalstyle(ivar)) {
+        lmp->input->variable->internal_set(ivar, value);
+        return 0;
+    }
+  }
+  END_CAPTURE
+  return -1;
+}
 
 /* ---------------------------------------------------------------------- */
 
diff --git a/src/library.h b/src/library.h
index 7db86bd71d..10cac6741a 100644
--- a/src/library.h
+++ b/src/library.h
@@ -177,7 +177,9 @@ void *lammps_extract_compute(void *handle, const char *, int, int);
 void *lammps_extract_fix(void *handle, const char *, int, int, int, int);
 void *lammps_extract_variable(void *handle, const char *, const char *);
 int lammps_extract_variable_datatype(void *handle, const char *name);
-int lammps_set_variable(void *handle, char *name, char *str);
+int lammps_set_variable(void *handle, const char *name, const char *str);
+int lammps_set_string_variable(void *handle, const char *name, const char *str);
+int lammps_set_internal_variable(void *handle, const char *name, double value);
 int lammps_variable_info(void *handle, int idx, char *buf, int bufsize);
 
 /* ----------------------------------------------------------------------
diff --git a/tools/swig/lammps.i b/tools/swig/lammps.i
index 91a6866107..b0670b40a4 100644
--- a/tools/swig/lammps.i
+++ b/tools/swig/lammps.i
@@ -129,11 +129,13 @@ extern void  *lammps_extract_global(void *handle, const char *name);
 extern int    lammps_extract_atom_datatype(void *handle, const char *name);
 extern void  *lammps_extract_atom(void *handle, const char *name);
 
-extern void  *lammps_extract_compute(void *handle, char *id, int, int);
-extern void  *lammps_extract_fix(void *handle, char *, int, int, int, int);
-extern void  *lammps_extract_variable(void *handle, char *, char *);
+extern void  *lammps_extract_compute(void *handle, const char *id, int, int);
+extern void  *lammps_extract_fix(void *handle, const char *, int, int, int, int);
+extern void  *lammps_extract_variable(void *handle, const char *, const char *);
 extern int    lammps_extract_variable_datatype(void *handle, const char *name);
-extern int    lammps_set_variable(void *, char *, char *);
+extern int    lammps_set_variable(void *, const char *, const char *);
+extern int    lammps_set_string_variable(void *, const char *, const char *);
+extern int    lammps_set_internal_variable(void *, const char *, double);
 
 extern void   lammps_gather_atoms(void *, char *, int, int, void *);
 extern void   lammps_gather_atoms_concat(void *, char *, int, int, void *);
@@ -312,11 +314,13 @@ extern void  *lammps_extract_global(void *handle, const char *name);
 extern int    lammps_extract_atom_datatype(void *handle, const char *name);
 extern void  *lammps_extract_atom(void *handle, const char *name);
 
-extern void  *lammps_extract_compute(void *handle, char *id, int, int);
-extern void  *lammps_extract_fix(void *handle, char *, int, int, int, int);
-extern void  *lammps_extract_variable(void *handle, char *, char *);
+extern void  *lammps_extract_compute(void *handle, const char *id, int, int);
+extern void  *lammps_extract_fix(void *handle, const char *, int, int, int, int);
+extern void  *lammps_extract_variable(void *handle, const char *, const char *);
 extern int    lammps_extract_variable_datatype(void *handle, const char *name);
-extern int    lammps_set_variable(void *, char *, char *);
+extern int    lammps_set_variable(void *, const char *, const char *);
+extern int    lammps_set_string_variable(void *, const char *, const char *);
+extern int    lammps_set_internal_variable(void *, const char *, double);
 
 extern void   lammps_gather_atoms(void *, char *, int, int, void *);
 extern void   lammps_gather_atoms_concat(void *, char *, int, int, void *);