The African Union on Saturday expressed concern over a 1991 ceasefire in the Western Sahara, disputed between Morocco and the pro-independence Polisaro Front, after Rabat sent troops to a buffer zone.
The AU chief's statement came as the Polisario Front declared the ceasefire was a "thing of the past" after Morocco launched an operation to reopen the road to neighbouring Mauritania, sparking clashes.
Chairman of the AU Commission Moussa Faki Mahamat expressed his "deep concern following the deterioration of the situation in the Western Sahara, especially in the buffer zone of Guerguerat, and the serious threats of breaching the ceasefire in force since 1991."
Morocco forces on Friday launched an operation at Guerguerat, the last Moroccan-held stop before the road enters a buffer zone along the border where the Polisario has maintained a periodic presence.
Faki also commended the efforts of the UN secretary-general and regional powers to urge "the parties to refrain from any change of the status quo and to return to the negotiating table, as soon as possible".
The United Nations has for days been trying to avoid an escalation in Western Sahara, and its chief Antonio Guterres has expressed "grave concern regarding the possible consequences of the latest developments".
Western Sahara's former colonial power Spain also called on "the parties to resume the negotiation process and move towards a political, fair, lasting and mutually acceptable solution."
In a statement released Friday evening, the Spanish foreign ministry called for "responsibility and restraint" in Western Sahara.
Morocco controls 80 percent of the disputed region, a vast swathe of desert on Africa's Atlantic coast.
The Polisario's forces are largely confined to the sparsely populated desert interior and refugee camps in neighbouring Algeria, the independence group's main foreign backer.
The Moroccan operation is aimed toward reopening the final section of the highway through Western Sahara to Mauritania by extending its network of defensive walls.
The defence ministry of the Polisario-declared Sahrawi Arab Democratic Republic (SADR) said its forces had carried out "massive attacks" on Friday at multiple points along Morocco's 2,700-kilometre (1,700 mile) defensive wall.
There was no immediate independent verification of the defence ministry's claim.
For its part, the Moroccan army general staff declared that "the Guerguerat crossing between Morocco and Mauritania has now been fully made safe by the installation of a security cordon by the Royal Armed Forces."