The pro-independence Polisario Front declared a three-decade-old ceasefire in disputed Western Sahara was over on Friday after Morocco launched an operation to reopen the road to neighbouring Mauritania
Rabat said its troops would "put a stop to the blockade" of trucks travelling between Moroccan-controlled areas of the disputed territory and neighbouring Mauritania, and "restore free circulation of civilian and commercial traffic".
The Polisario Front had warned on Monday that it would regard a three-decade-old ceasefire with Morocco as over if Rabat moved troops or civilians into the buffer zone.
"War has started, the Moroccan side has liquidated the ceasefire," senior Polisario official Mohamed Salem Ould Salek told AFP, describing the action by Rabat as an "aggression".
"Sahrawi troops are engaged in legitimate self-defence and are responding to the Moroccan troops," said Ould Salek, who serves as foreign minister of the Polisario-declared Sahrawi Arab Democratic Republic.
Algeria, a key-backer of Polisario, and Mauritania urged restraint. "Algeria calls on both parties, the Kingdom of Morocco and the Polisario Front, to show a sense of responsibility and restraint," Algeria's foreign ministry said in a statement on Friday.
Mauritania's foreign minister also urged "all protagonists to work towards the preservation of the ceasefire".
Polisario secretary-general Brahim Ghali has written to UN chief Antonio Guterres calling for the Security Council "to intervene urgently to put an end to this aggression against our people and our territory", Ould Salek said.
"This will also mean the end of the ceasefire and the beginning of a new war across the region," the Polisario said in a statement.
But the Moroccan foreign ministry said it had been forced to act by the actions of Polisario fighters and the failure of its own appeals and those of the UN peacekeeping mission MINURSO.
"The Polisario and its militias, who have infiltrated the zone since October 21, have been carrying out acts of banditry, blocking traffic and continually harassing MINURSO military observers," a ministry statement said.
A senior ministry official contacted by AFP said that for some three weeks, around 70 armed men had been "attacking truck drivers, blocking their passage and engaging in extortion".
Nearly 200 truck drivers with vehicles from different countries including France, Morocco and Mauritania are stranded on the Mauritanian side of the border and 78 on the other side, the official said.
They appealed to both Rabat and Nouakchott for help returning home after "Polisario fighters" blocked their passage.
They urged UN peacekeepers to "play their role in protecting the buffer zone and the border crossing, which provides a gateway for work for thousands of drivers, farmers and traders".
Western Sahara, a vast swathe of desert on Africa's Atlantic coast, is a disputed former Spanish colony.
Rabat controls 80 percent of the territory, including its phosphate deposits and its lucrative ocean fisheries.
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.
Peacekeeping force MINURSO has patrolled a buffer zone between the two sides since a UN-brokered ceasefire took effect in 1991.
The village of Guergerat in the far south of the Western Sahara is the last village under Moroccan control.
Beyond it is a strip of desert where Polisario fighters have maintained a periodic presence in recent years.
An informal trade has grown up exporting Moroccan fresh produce to the Mauritanian coastal city of Nouadhibou, but to the growing anger of Rabat it has periodically fallen foul of the Polisario.
Morocco, which maintains that Western Sahara is an integral part of the kingdom, has offered autonomy for the territory but insists it will retain sovereignty.
The Polisario demands a referendum on self-determination as set out in the 1991 ceasefire.
The planned referendum has been repeatedly postponed due to disputes between Rabat and the Polisario over voter rolls and the question to be put.
Negotiations on the territory's future involving Morocco, the Polisario, Algeria and Mauritania have been suspended for some time.
(FRANCE 24 with AFP)