Morocco on Wednesday hinted it could act unilaterally if the United Nations and Algeria fail to stop Polisario Front fighters it accuses of carrying out incursions into a buffer zone.
"If the security council does not assume its responsibilities, Morocco will assume its own," Foreign Minister Nasser Bourita said after a meeting with UN chief Antonio Guterres.
He said that Morocco's King Mohammed IV spoke with Guterres directly, expressing "Morocco's clear firm and determined rejection of these provocations, these incursions, by Polisario" into a Western Sahara buffer zone where the UN is responsible for supervising a ceasefire.
Morocco wrote to the Security Council on Sunday to report that fighters of the Polisario Front had entered the northeastern Western Sahara town of Mahbes in recent days in violation of a military agreement setting up the buffer zone.
The fighters turned up in "military vehicles, and have set up tents, dug a ditch and built constructions using sandbags," Morocco's UN Ambassador Omar Hilale said in the letter, a copy of which was obtained by AFP.
Asked about the Moroccan claims, UN spokesperson Stephane Dujarric said the MINURSO mission had "not observed any movement of military elements in the northeast territory."
Polisario has also denied the Moroccan accusations.
"These actions constitute a threat to the cease-fire" and "seriously compromise the peace process," Bourita told a news conference.
He said that Algeria "has a blatant responsibility" in the multi-decade conflict, and that Morocco demands Algiers "take an important part in the political process, assume its responsibilities in the search for a solution and play a role equal to its responsibility in the genesis of this regional dispute."
The minister brandished documents and aerial photographs he said proved Polisario's creation of "many" military installations between August 2017 and March 2018.
Rabat considers Western Sahara an integral part of Morocco and proposes autonomy for the resource-rich territory, but the Polisario Front insists on a UN referendum on independence.
Morocco and the Polisario fought for control of Western Sahara from 1975 to 1991.