UNITED NATIONS - UN Secretary-General Ban Ki-moon was "deeply concerned" over the rising tension in southwestern Western Sahara, said Ban's spokesman on Sunday.

The tense situation occurred as a result of changes in the status quo and the introduction of armed units from Morocco and the Polisario Front, which is supported by Algeria, said the spokesman in a statement.

"The secretary-general calls on both parties to suspend any action that alters that status quo and to withdraw all armed elements so as to prevent any further escalation and permit MINURSO (the UN Mission for the Referendum in Western Sahara) to hold discussions with both parties on the situation," the statement said.

Ban asked both parties to adhere to their obligations under a 1991cease-fire agreement, it said.

Since 1979, most of the territory of Western Sahara has been under the de facto control of Morocco, and the rest part by the Polisario Front.