The militant Polisario Front, seeking independence for Western Sahara, said Morocco had violated the ceasefire in the disputed territory on Saturday.
The claim came in a letter to Claude Bize, commander of the military section of the United Nations Mission in Western Sahara (MINURSO), a copy of which reached AFP in Algiers.
Polisario had earlier warned drivers in the Paris-Dakar car rally to stay away from the territory on Sunday if they valued their lives.
The letter from Mohamed Lamine Bouhali, defense minister of the self-proclaimed Sahrawi republic, said that on Saturday "a rapid intervention detachment of the Moroccan armed forces left the defensive wall over a distance of five kilometers heading for the Mein Terguet zone.
"This was a flagrant violation of the ceasefire which we draw to your attention and which calls for a strong reaction."
A 35-kilometer (22-mile) buffer zone between Morocco and Polisario separates the two sides beyond a defensive wall built by the Moroccan army in the 1980s to prevent Polisario "infiltrations".
On Friday, Bize told AFP that MINURSO would "watch that neither Morocco nor the Polisario Front has a military presence in the 35-kilometer security zone.
"I will verify on the ground, with observers and with all means at my disposal that the (ceasefire) accord is respected," he said.
The Paris-Dakar rally was scheduled to enter the Moroccan-occupied territory on Sunday.
A spokesman for Polisario said the planned route through the Western Sahara was a violation of a 1991 ceasefire between the front and Morocco, "prompting an immediate response in legitimate defense and the resumption of military action."
Competitors in the rally -- a highlight of the sports calendar -- left Paris on January 1 and were to scheduled to cross the "frontier" during the 489-kilometer (313-mile) seventh stage, a desert route from Goulimine in southern Morocco to Smara in the Western Sahara protected by the wall -- ALGIERS (AFP)
