King Mohammed VI of Morocco reviews a guard of honour at the National palace during his state visit to Ethiopia's capital Addis Ababa, November 19, 2016. REUTERS/Tiksa Negeri

RABAT (Reuters) - Morocco’s King Mohammed VI has called on the United Nations to take “urgent measures” following months of tensions with the Polisario independence movement in the disputed Western Sahara region.

The king talked with U.N. Secretary General Antonio Guterres, denouncing the Polisario Front, which for decades has sought self-determination for the desert region, according to a royal cabinet statement on MAP state news agency late Friday.

During a telephone call, King Mohammed pointed to the “repeated incursion of armed Polisario elements and their acts of provocation” in Guerguerat, an area in disputed Western Sahara near Mauritania.

Polisario declared an independent republic in the disputed desert land in the 1970s and fought a guerrilla war with Morocco until a 1991 ceasefire. The group accuses Rabat of breaking the terms of the ceasefire last year by trying to build a road in the U.N. buffer zone. Morocco says it was just a road clearing operation that broke no terms of the ceasefire.

The standoff in Guerguerat last year forced U.N. troops to step in after Moroccan gendarmerie crossed past an earthen wall marking Moroccan-controlled areas and the Polisario responded in kind. Their units remain facing each other less than a kilometer apart.

During the call with Guterres, the king described the situation as “seriously threatening the ceasefire and putting regional stability at risk”.

For the Polisario Front, Morocco is to blame for what they describe as a “critical and dangerous situation”.

“Morocco wants to construct this road in Guerguerat that involves the annexation of territory that is beyond the Moroccan wall,” the Polisario Front Coordinator with the U.N., M’hamed Khadad, told Reuters. “It is Morocco that should take entire responsibility for this crisis.”

Rich in phosphate, Western Sahara has been contested since 1975 when Spanish colonial powers left. Morocco claimed the territory and fought the 16-year war with Polisario before signing the U.N. ceasefire that foresaw a referendum on self-determination. But that vote has never happened.