The pro-independence Polisario Front on Friday said a 30-year-old cease-fire in disputed Western Sahara ended after Morocco launched an operation in a border area.

"War has started, the Moroccan side has liquidated the cease-fire," senior Polisario official Mohamed Salem Ould Salek told the AFP news agency.

The Moroccan military early on Friday started an operation to clear the road in the Guerguerat area, linking to neighboring Mauritania, which it said had been blockaded for weeks by supporters of the Polisario Front.

The road, located in an UN-monitored buffer zone in the far south of Western Sahara, links the Morocco-controlled territory to neighboring Mauritania.

Rabat said the operation was launched to "put a stop to the blockade" of trucks traveling between the Western Sahara and Mauritania and restore movement.

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A Polisario official accused Moroccan troops of firing at innocent protesters and said Polisario fighters came to their defense, prompting "intense clashes" on Friday.

"Sahrawi troops are engaged in legitimate self-defense and are responding to the Moroccan troops," Ould Salek said.

The Polisario Front said the 1991 cease-fire, which it warned this week was hanging by a thread, came to an end with the Moroccan military action.

UN expresses "grave concern"

UN Secretary-General Antonio Guterres was committed to doing the utmost to avoid the collapse of the cease-fire, his spokesperson Stephane Dujarric said on Friday.

Guterres and other UN officials have been making phone calls and been involved in "multiple initiatives to avoid an escalation," Dujarric said.

"The Secretary-General regrets that these efforts have proved unsuccessful and expresses grave concern regarding the possible consequences of the latest developments," Dujarric added.

However, "the secretary-general remains committed to doing his utmost to avoid the collapse of the cease-fire that has been in place since September 6, 1991, and he is determined to do everything possible to remove all obstacles to the resumption of the peace process," he said.

Neighboring Algeria, which backs the Polisario, called on both sides to exercise restraint.

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Mauritania also called for "all protagonists to work towards the preservation of the cease-fire."

Morocco annexed Western Sahara, a former Spanish colony, in 1975 and has since controlled 80 percent of its territory, including its phosphate deposits and its lucrative ocean fisheries.

The region also gives Morocco access to the rest of Africa, as its borders with Algeria have been closed for decades.

Polisario Front forces are confined to the sparsely populated desert regions near the Algerian border.

The pro-independence group has called for a referendum on self-determination that was set out in the 1991 cease-fire but never took place due to disputes with Rabat over voter rolls and the phrasing of the question to be asked.

Morocco has offered autonomy for the territory but insists it will retain sovereignty over the region.

adi/sms (AP, AFP, Reuters)