Turkish artillery fire from the border near Kilis toward northern Syria, in Kilis, Turkey on Monday. (Halit Onur Sandal/AP)

The deadline for a cease-fire in Syria’s civil war came and went Friday, as joint diplomatic and military teams from the United States and Russia tried to agree on rules covering where the shooting would stop and where it would be allowed to continue.

The closed-door talks in Geneva were the first face-to-face meeting between high-level U.S. and Russian military officials over Syria since Russia began bombing there in the fall on behalf of President Bashar al-Assad.

Amid growing chaos on and around the northwest Syrian battlefield where myriad fighting forces­ have converged, an emergency meeting of the U.N. Security Council was convened in response to Russian demands to stop what it said were Turkey’s plans “to put boots on the ground” in the area.

The cease-fire, initially set for Friday, was part of an agreement reached a week ago in Munich by the United States, Russia and other outside stakeholders in the Syrian conflict to stop a situation that appears to be rapidly spiraling out of control.

The United States, Russia and other powers came to an agreement on a ‘cessation of hostilities’ in Syria, but the deal was met with caution and skepticism. (Jason Aldag,Ishaan Tharoor/The Washington Post)

Secretary of State John F. Kerry expressed confidence that the Geneva talks were proceeding along the right track.

“Everyone recognizes the complexity of this endeavor, and there is certainly a lot more work to do,” Kerry said in a statement. “These discussions have been serious and so far constructive, with a few tough issues still to resolve.”

Several proposals for a new cease-fire deadline — all centered on dates in the coming week — had been tabled, according to Obama administration officials, who spoke on the condition of anonymity because they were not authorized to discuss the matter.

The U.S. team, headed by senior White House adviser Robert Malley and State Department envoy Brett McGurk, included officers from the Pentagon’s Joint Staff, the Special Operations Command and the Central Command.

The meeting marked a de facto suspension of the administration’s refusal to coordinate military actions in Syria outside of “deconfliction” talks to avoid an encounter between U.S. and Russian aircraft in increasingly crowded skies. The United States has been striking Islamic State targets in Syria since September 2014. For the past five months, Russia has been launching strikes against U.S.-supported opposition groups fighting against Assad.

Defense Secretary Ashton B. Carter was said to have opposed the high-level contact with the Russians, at least initially. But Kerry and others in the administration argued that the subject matter demanded military expertise.

The cease-fire is called a “cessation of hostilities” in the Munich agreement among 17 nations that are supporting one side or the other in the Syrian civil war. In addition to the survival of the U.S.-backed Syrian opposition — under a barrage of Russian air attacks that have only increased since the cease-fire plan was signed — and hopes that an end to the fighting would facilitate talks about a political transition, the administration has been concerned about the safety of several dozen Special Operations troops deployed inside Syria as part of its separate fight against the Islamic State.

Under the terms of the Munich deal, the United States and Russia are co-chairs of a task force to work out the terms of a cease-fire, including where airstrikes against “terrorist” groups are permitted to continue and how to resolve violations.

Each side is also supposed to bring its proxies on board, with Russia and Iran responsible for Assad’s forces­ and Shiite militias from Iraq and Hezbollah that are fighting alongside them, and the United States and its European and Middle Eastern partners in charge of securing agreement from the opposition.

One of the many problems to be overcome is a differing definition of what constitutes a terrorist group. In addition to the Islamic State and Jabhat al-Nusra, al-Qaeda’s affiliate in Syria, Russia and Syria have labeled the entire opposition as terrorists.

Jabhat al-Nusra, whose forces are intermingled with moderate rebel groups in the northwest near the Turkish border, is particularly problematic. Russia was said to have rejected a U.S. proposal to leave Jabhat al-Nusra off-limits to bombing as part of a cease-fire, at least temporarily, until the groups can be sorted out.

The decision by the United States and Russia to hold a preparatory meeting by themselves, without inviting the other 15 members of the group, led to confusion early Friday and reports that the broader meeting had been canceled before it even began.

Any agreement they reach must be presented to the entire group, some members of which are likely to disapprove of parts of whatever the two chairs decided.

A separate task force, established in Munich to press for humanitarian access to communities in Syria besieged by the fighting, brought aid to five areas this week. Jan Egeland, an adviser to Staffan de Mistura, the U.N. special envoy for Syria, said in a statement Thursday that all remaining areas should be reached before that task force meets again next week.

Both the cease-fire and the humanitarian agreements are intended to clear the way for peace talks between the Assad government and the opposition. In an interview with the Swedish newspaper Svenska Dagbladet, de Mistura indicated that it was unlikely those talks would resume as scheduled on Thursday.

“We need real talks about peace, not just talks about talks,” de Mistura was quoted as saying in remarks that were published Thursday and translated by the Associated Press.

Meanwhile, the growing crisis among Russia, Turkey and the United States threatened to overshadow the cease-fire plans. Turkey, Saudi Arabia and the United Arab Emirates — all opposition supporters — have said they would send ground troops into Syria, but only as part of a plan by the U.S.-led coalition against the Islamic State, a plan that does not yet exist.

At the same time, Turkey has said it will not stop cross-border shelling of Syrian Kurdish forces­ it says are in league with both Russia and Assad to take over Syrian territory along its border, and with Turkey’s outlawed Kurdistan Workers’ Party, the PKK, which both Turkey and the United States have designated as a terrorist group.

Friday’s closed-door Security Council meeting was adjourned until Monday after considering a proposed Russian resolution against Turkey. In November, Turkey shot down a Russian jet that it said had strayed into its airspace from Syria.

Turkey’s U.N. ambassador, Yasar Halit Cevik, told reporters after the meeting that “Turkey will not be going into Syria with boots on ground if [it is] not a collective action” authorized by the United Nations or the U.S.-led coalition against the Islamic State.

But he said the United States was mistaken in its belief that Syria’s Democratic Union Party, a Kurdish group, was fighting against the Islamic State in northwestern Syria.

“They are not fighting [the Assad] regime or Daesh,” Cevik said, using an Arabic acronym for the Islamic State. “The area they have captured was not from Daesh or al-Nusra, it was captured from the Syrian opposition. The fire is coming from Syrian soil and, based on our rules of engagement, we are retaliating.”

Michael Birnbaum in Moscow, Hugh Naylor in Beirut and Carol Morello in London contributed to this report.

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