From Crisis Group's latest report: https://www.crisisgroup.org/middle-east-north-africa/north-africa/western-sahara/b82-time-international-re-engagement-western-sahara

After almost 30 years of compliance with a 1991 ceasefire, Morocco and the Polisario Front have resumed hostilities in Western Sahara, a disputed territory for which the Front seeks independence. On 13 November 2020, Morocco sent troops into the UN-monitored buffer zone to end Polisario supporters’ three-week blockade of the strategic Guerguerat road. In response, Polisario withdrew from the ceasefire and renewed attacks on Moroccan military units. International reactions to the escalation have mostly been sympathetic to Morocco. The UN Security Council has remained silent. Rabat scored a major diplomatic victory on 10 December, when U.S. President Donald Trump recognised its sovereignty over Western Sahara. To avoid escalation, Morocco’s international backers should push Rabat to accept the appointment of a new UN special envoy – a position vacant since May 2019 – without preconditions. The Biden administration, in close coordination with France, Russia and Algeria, all primary external stakeholders in the conflict, should press both sides to accept a truce and restart talks.

Just two years ago, things looked very different. Diplomacy seemed to be moving along, thanks to the August 2017 appointment of former German President Horst Köhler as UN special envoy. In April 2018, the UN Security Council reduced the time between mandate renewals for the UN Mission for the Referendum in Western Sahara (MINURSO) from one year to six months; the envoy thus reported more frequently on the situation to the Council, which upped pressure on both sides. Morocco, the Polisario Front, Algeria and Mauritania held two meetings that showed signs of progress. But Köhler’s sudden resignation in May 2019 and the Council’s October 2019 reversion to one-year MINURSO mandates halted the momentum. Since then, both Morocco and Polisario have placed preconditions on the appointment of a new envoy to replace Köhler, with Rabat’s stricter requirements seemingly causing a stalemate.

Tensions started to build up in the Guerguerat area, where a road connecting Morocco to Mauritania crosses the UN-monitored buffer strip separating Moroccan troops from Polisario fighters. Taking advantage of the diplomatic void left after Köhler’s departure, Morocco invited several African and Middle Eastern governments to open consulates inside Western Sahara. In response, Polisario officials and activists promptly labelled the move a return to war. Civilian Polisario supporters (joined by gunmen) blockaded the main road through Guerguerat, establishing a camp in late October 2020 and sparking a resumption of hostilities. On 13 November, Morocco sent troops inside the buffer strip to remove the blockade. In response, Polisario initiated a low-intensity conflict with Morocco, even though Rabat reaffirmed its support for the ceasefire’s continuation.

Most international actors supported returning to the ceasefire or fell in behind Morocco. At the same time, the UN Security Council refrained from discussing the flare-up, frustrating Polisario’s goal of attracting world attention to its cause. Rabat saw the 10 December U.S. recognition of Moroccan sovereignty over Western Sahara as additional vindication of its strategy. The Trump administration’s move further antagonised pro-independence Sahrawis, especially Sahrawi youth, who have long been losing faith in a diplomatic solution to the conflict.

The conflict’s low intensity cannot be an excuse for inaction. There is a modest but palpable risk of a gradual military escalation, which could further destabilise North Africa and the Sahel. Heavier fighting could be triggered by a military incident, Algerian interference – for example, stepped-up weapons transfers from Algiers to Polisario – or a shift in the independence movement’s military tactics. To minimise this risk, Morocco’s external allies – the U.S. and France – should push Rabat to accept without preconditions a new UN envoy tasked with negotiating a de-escalation that could yield talks about a truce.

Such an approach would work only if the U.S. and the UN Security Council take a more hands-on approach. The Biden administration may shy away from undoing Trump’s recognition of Moroccan sovereignty over Western Sahara. But even short of that, it could pursue other ways of reassuring Polisario, for example by reverting to Washington’s earlier support for a semi-annual MINURSO mandate renewal. To avoid antagonising Morocco, UN Security Council resolutions should contain explicit reference to the need to protect the Guerguerat road as a safe thoroughfare. These arrangements could usher in a new phase for diplomacy. The Biden administration should coordinate its position more closely and transparently with other countries with a stake in the conflict’s outcome, namely France, Russia and Algeria. Better cooperation at this level could end the fighting and jump-start stalled peacemaking efforts.