Tensions in the former Spanish colony have sparked concern around the globe, with the United Nations, the African Union, Algeria and Mauritania urging both sides to respect a 1991 ceasefire.

But Saturday Mohamed Salem Ould Salek, a foreign minister of the Polisario-declared Sahrawi Arab Democratic Republic (SADR), said the UN-supervised ceasefire was a "thing of the past".

"Fighting is continuing after the crime committed by Moroccan troops in Guerguerat," he told AFP.

Later in the day, the SADR defence ministry said that the regions of Mahbes and Guerguerat had been "targeted by shells and machine gun" fire.

The claim could not be independently verified.

Polisario secretary-general Brahim Ghali said he had issued a decree Friday announcing the end of its obligations under the ceasefire agreement and "the resumption of armed actions in order to protect the inalienable rights of our people."

On Friday, Morocco announced that it had launched a military operation in the buffer zone of Guerguerat to reopen the highway to Mauritania, accusing the Polisario of blocking the road.

Pictures released by the Moroccan army showed tents reportedly used by the Polisario on fire near the Mauritania border after the operation.

Dozens of truck drivers had been stranded for days at Guerguerat.

But on Saturday traffic resumed, with 80 trucks crossing into the Western Sahara from Mauritania, a Mauritanian security source said.

A senior Moroccan official told AFP that traffic had resumed in both directions.

The road is key for trade with the rest of Africa.

- Calls for restraint -

On Friday, the SADR defence ministry said "massive attacks" had been carried out at multiple points along Morocco's 2,700 kilometre (1,700 mile) long defensive wall.

It said they had inflicted "human and material damage on the enemy".

The claim was denied in Rabat by a "well-informed source", who said that Morocco's army chief of staff and the UN's MINURSO mission did not report any attacks.

Morocco's military said on Friday it had secured the Guerguerat crossing between Morocco and Mauritania by installing "a security cordon" along its desert wall.

Stephane Dujarric, spokesman for the UN chief, said that MINURSO deployed in Guerguerat "a special civil-military team... since the beginning of the crisis" and military observers were there overnight.

The unrest in Western Sahara has sparked concern around the world.

UN Secretary-General Antonio Guterres has expressed "grave concern regarding the consequences of the latest developments" that erupted despite UN efforts to avoid an escalation.

The Sahrawi news agency, SPS, reported that Guterres had spoken by phone with a senior Polisario leader on Friday.

Algeria, the Polisario's main foreign backer, and Mauritania have called for restraint and respect of the 1991 ceasefire.

Those calls were echoed by the African Union, France, Russia and Spain.

- 'Avoid escalation' -

AU Commission chairman Moussa Faki Mahamat expressed his "deep concern" while Spain, Western Sahara's former colonial power, urged the parties to resume negotiations for a "lasting solution".

France called on all sides to "avoid an escalation" and Russia urged them "to refrain from taking steps that can exacerbate the situation".

Gulf powerhouse Saudi Arabia, as well as Qatar, the United Arab Emirates and other Arab countries, have expressed support for Morocco in the conflict.

Rabat controls 80 percent of the Western Sahara -- a vast swathe of desert on the Atlantic coast -- including its phosphate deposits and its lucrative ocean fisheries.

Morocco maintains that Western Sahara is an integral part of the kingdom and has offered autonomy for the disputed territory, but insists it will retain sovereignty.

The Polisario demands a referendum on self-determination as set out in the 1991 ceasefire.

The vote has been repeatedly postponed due to disputes between Rabat and the Polisario over voter rolls and the question to be asked.