Facing an escalating civil war in Syria, the Security Council decided Thursday to end the U.N. military observer mission that was sent to monitor a cease-fire that never happened and back a small new liaison office that will support any future peace efforts.

Members who have been deeply divided on tackling the 18-month conflict were united behind U.N. Secretary-General Ban Ki-moon's proposal to replace the 300 unarmed observers with a small group of military advisers and political, human rights and civil affair experts, France's U.N. Ambassador Gerard Araud, the current Security Council president, announced.

The council agreed that conditions set for possibly extending the observer mission — a significant reduction in violence and an end to the Syrian government's use of heavy weapons — had not been met and its mandate would end Sunday, he said.

Araud said it was essential politically to have all 15 members on the divided council agree to approve the new liaison office, especially in light of the seriousness of the crisis which the U.N. says has killed at least 18,000 people.

"What is the most important is there will be a U.N. presence, and we hope useful U.N. presence," he said.

In a surprise follow-up, Russia's U.N. Ambassador Vitaly Churkin invited U.N. ambassadors from key nations and international organizations who agreed on guidelines for a Syrian-led political transition in Geneva in June to a meeting at U.N. headquarters Friday to press for action.

Churkin, whose country is the most important ally of Syrian President Bashar Assad, told reporters he wants the Geneva action group — along with Iran and Saudi Arabia, who are not members — to make "a joint or parallel appeal to all the parties of the Syrian conflict that they end violence as soon as possible by a certain point in time."

Churkin said the appeal should also urge the government and opposition to appoint representatives "to negotiate towards a political solution, and in particular towards the establishment of a transitional governing body as provided for in the Geneva document."

In a letter to the council last Friday, Ban said the conditions for extending the observer mission had not been met, but he added that the U.N. must maintain a presence in Syria in order to support international efforts to broker peace.

The Security Council initially authorized the observer mission to deploy to Syria for 90 days to monitor implementation of a six-point peace plan brokered by U.N.-Arab League envoy Kofi Annan. The plan was to start with a cease-fire and withdrawal of the government's heavy weapons and culminate with Syrian-led political talks.

Assad's government and opposition forces agreed to the plan, but it was never implemented.

Because of the worsening bloodshed, the observers have been mainly confined to their hotels since June 15, and their numbers have been cut by about two-thirds.

U.N. Assistant Secretary-General for Peacekeeping Edmond Mulet told reporters after briefing the council behind closed doors that the observer mission "will come to an end at midnight Sunday."

There are now 101 observers and 72 civilian staff members in Syria, he said. The last observers will leave on Aug. 24, though they will stop work after Sunday, he added.

Mulet said discussions are underway on the new liaison office, which he said has been approved by the Syrian government and will have about 20-30 staff members.

"It is clear that both sides have chosen the path of war ... and the space for political dialogue and cessation of hostilities and mediation is very reduced at this point," Mulet said, "but that doesn't mean ... we shouldn't face that challenge of trying to open those political spaces in the future."

Frustrated at the escalating conflict and the failure of world powers on the Security Council to unite to stop the chaos, Annan announced last month that he was resigning effective Aug. 31.

Russia and China have vetoed three Western-backed Security Council resolutions that would have stepped up pressure especially against the Syrian government by threatening sanctions if the fighting didn't stop.

Mulet said he expected an announcement of a replacement for Annan "very soon."

On Tuesday, a spokesman for Annan said Syrian authorities have backed former Algerian Foreign Minister Lakhdar Brahimi, a veteran U.N. troubleshooter in hotspots including Afghanistan and Iraq, as his successor, but it was unclear whether Brahimi had accepted the post.

Several U.N. diplomats, speaking on condition of anonymity because no announcement has been made, said Brahimi wants a signal of support from the council. What kind of support Brahimi wants remains unclear.

France's Araud said he would be sending Ban a letter, obtained by the Associated Press, that reiterates the council's support to Ban's "good offices and to the mission of the joint special envoy to Syria."

While the Security Council united behind Ban's proposals, Russia's Churkin criticized the U.S. and its European allies who opposed an extension of the observer mission.

The Action Group for Syria that met in Geneva in June included Ban, Arab League Secretary General Nabil Elaraby, the five permanent Security Council nations — the U.S., Russia, China, France and Britain — Turkey, Iraq which chairs the Arab League summit, Kuwait which chairs the Arab League's council of foreign ministers, Qatar which chairs the Arab League's follow-up committee on Syria, and the European Union foreign police chief.

Several countries said they hadn't received invitations and were seeking further information and advice from their capitals.

Churkin said Russia has made "no secret" of its criticism of some members that have done little if anything to implement the document adopted by the action group to promote a political dialogue.

If Moscow is wrong about this, he said, Friday's meeting "is a good time to prove us wrong."


Associated Press Writer Ron DePasquale contributed to this report from the United Nations