The fragile truce that had lasted since 1991 in Western Sahara has collapsed as the Moroccan military launched an operation in a UN-manned buffer strip in the disputed Guerguerat border zone.

The Moroccan military stated that the operation was launched to clear a key road that had been blocked since October 21, following weeks of “provocations,” by supporters of the pro-independence Polisario Front.

The road cuts across the UN buffer strip towards the border between Western Sahara and Mauritania; it links Morocco to Mauritania. The road is the primary access highway for the movement of goods and people between the two countries.

The Polisario Front considers the road illegal since it says it was built in violation of the 1991 truce.

The Moroccan Ministry of Foreign Affairs had accused the Polisario of carrying out “acts of banditry” and “harassing” UN peacekeeping forces operating in the region.

A spokesman for the Polisario Front accused the Moroccan military of firing at innocent protesters something that led to clashes between Moroccan and Polisario forces on Friday. 

“War has started, the Moroccan side has liquidated the ceasefire,” senior Polisario official Mohamed Salem Ould Salek told the media, calling the Moroccan operation an “aggression.”

Tensions in the region date to 1975 when Morocco annexed Western Sahara, a former Spanish colony that was also briefly occupied by Mauritania. Western Sahara is believed to have rich offshore oil and mineral deposits. For years, the Polisario fought for independence from Morocco in a struggle that lasted until 1991, when the United Nations negotiated an armistice between the two parties.

The UN established a peacekeeping mission to monitor the truce and aid in the preparation of a referendum whereby the territory’s indigenous people, known as Sahrawis, would choose between independence or integration with Morocco. That referendum never took place.

Many of the Sahrawis now live in a refugee camp on the Algerian border. 

The Moroccan government has vowed to give far-ranging autonomy to Western Sahara. Yet, the Polisario Front has rejected the overtures arguing instead for a referendum. 

UN spokesman Stephane Dujarric said that UN officials have been working to propose “multiple initiatives to avoid an escalation;” thus far they have been unsuccessful. He added that UN officials had been seeing the warning signals for quite some time.

When asked who was responsible for the latest fighting he replied: “We have seen over the last few weeks violations from both sides. We have condemned, and we condemn all violations of the ceasefire.”

On Friday, the Moroccan Royal Armed Forces General Staff released a statement saying that Moroccan forces have set up a security cordon in the Guerguerat buffer zone “in order to secure the flow of goods and people through this axis.” It didn’t specify the number of troops involved.

Brahim Ghali, the secretary-general of the Polisario Front, characterized the Moroccan operation as an “act of aggression and a flagrant violation of the ceasefire” that came into place in September 1991.

In a letter to the United Nations Secretary-General António Guterres, he wrote that by launching the operation Morocco has undermined “any chances of achieving a peaceful and lasting solution to the decolonization question of Western Sahara.” Copies of the letter were reportedly posted on media outlets but haven’t yet been confirmed.

Morocco stated on Friday that it had apprised the United Nations and neighboring countries of its military plans. In a statement, the Moroccan foreign ministry said it had “no other choice but to assume its responsibilities in order to put an end to the deadlock situation.”