UNITED NATIONS (AP) — Morocco's foreign minister warned Wednesday that all options are on the table including military action if the United Nations doesn't act against Polisario Front construction and plans for military posts in U.N.-monitored buffer zones in Western Sahara.

Nasser Bourita said at a news conference that the cease-fire implemented in 1991 is threatened by the recent actions of the Polisario Front, which seeks independence for mineral-rich Western Sahara.

"Morocco is saying very clearly that all the options are under consideration," Bourita said. "Morocco will not allow a change on the ground. If the U.N., the international community, don't take their responsibilities, Morocco will take its own responsibility."

The Polisario Front's U.N. representative, Ahmed Boukhari, earlier this week rejected Morocco's charges as "unfounded and false." He told the Security Council in a letter Monday that the U.N. peacekeeping force in Western Sahara has not reported any cease-fire violations by the independence movement.

Boukhari accused Morocco of seeking to change the status quo by constructing a road across the buffer zone in the Guergerat area. He also called Morocco's latest allegations "a smoke screen" to divert the Security Council's attention from the issues underlying the current stalemate over Western Sahara.

Algeria's official APS news agency published a Polisario Front statement Wednesday saying Boukhari died Tuesday in Spain at age 64 after a long illness.

Morocco annexed Western Sahara, a former Spanish colony, in 1975 and fought the Polisario Front. The U.N. brokered the cease-fire in 1991 and established a peacekeeping mission to monitor the truce and help prepare a referendum on the territory's future. That vote has never taken place.

Morocco considers the mineral-rich Western Sahara its "southern provinces" and has proposed giving the territory wide-ranging autonomy. The Polisario Front insists on self-determination through a referendum for the local population, which it estimates at between 350,000 and 500,000.

Bourita said he met with U.N. Secretary-General Antonio Guterres on Wednesday and gave him a letter from King Mohammed VI who also spoke to the U.N. chief by phone.

"The king underlined that there should be a solution to this issue very soon," the foreign minister said. "Otherwise, Morocco will take its responsibilities."

Bourita said he shared "facts and evidence" during a "serious" and "constructive" meeting with Guterres, including satellite photos taken March 26 and March 29 that he said show Polisaro construction in the buffer zone.

He said he also presented announcements by the Polisaro Front in March that it was transferring what Bourita called its "so-called presidency" to the buffer zone and establishing military installations there.

Bourita, who also met with the Security Council president, said the U.N. is responsible for maintaining the cease-fire and it should react to the "real and serious threat to that cease-fire." The mandate for the U.N. mission in Western Sahara, known as MINURSO, expires in late April but is expected to be renewed.

Bourita said he was encouraged by steps taken by the secretary-general's new personal envoy for Western Sahara, former German President Horst Koeler, to relaunch political negotiations with the Polisario Front.

But he stressed that for the political process to be successful, Algeria must be included as a party because it hosts, arms, finances and diplomatically supports the Polisario Front.