MUNICH — Diplomats trying to secure a ceasefire for the civil war in Syria fell short in organizing an immediate truce but agreed to try to work out details and implement a temporary "cessation of hostilities" in the coming week.

Foreign ministers from the International Syria Support Group also sealed an agreement early Friday to "accelerate and expand" deliveries of humanitarian assistance to seven besieged Syrian communities. Those deliveries are to begin immediately after a working group meets on the matter Friday in Geneva.

Speaking for the group, U.S. Secretary of State John Kerry hailed the results but noted they were "commitments on paper."

"The real test is whether or not all the parties honor those commitments and implement them," he said.

Kerry and Russian Foreign Minister Sergey Lavrov, who had been pressing for a ceasefire to begin March 1, said the U.S. and Russia would co-chair both the working group on humanitarian aid as well as the group that will try to deal with the "modalities" of the temporary truce. However, it was not clear if deep and festering differences between the U.S. and Russia on these issues could be overcome.

While humanitarian access is critical to relieving the suffering of millions of Syrians in the short term, a durable and lasting ceasefire will be required if stalled negotiations between Syrian President Bashar Assad's government and the opposition are to resume on or before the U.N.-set target date of Feb. 25. The talks broke down last month before they really started, due largely to gains by Assad's military with the heavy backing of Russian airstrikes.

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Russia had proposed the March 1 ceasefire, but the U.S. and others saw that as a ploy to give Moscow and the Syrian army three more weeks to try to crush Western- and Arab-backed rebels. The U.S. countered with demands for an immediate stop to the fighting. Both countries appeared to have made concessions on that front.

Despite the concession on potential timing of the truce and the agreement to set up the task force, the U.S., Russia and others remain far apart on which groups should be eligible for it. The new task force, which will include military officials, will take up a job that was supposed to have been settled months ago. At the moment, only two groups — the Islamic State group and the al-Qaida-affiliated al-Nusra Front — are ineligible for the truce because they are identified as terrorist organizations by the United Nations.

Russia, Syria and Iran argue that other groups, notably some supported by Turkey, Saudi Arabia and some other Arab states, should not be eligible for the ceasefire, and there was no sign Friday that those differences had been resolved.

Lavrov said the Russian air campaign in support of Assad's military would continue against terrorist groups.

U.S. Secretary of Defense Ash Carter speaks during a media conference at NATO headquarters in Brussels on Thursday, Feb. 11, 2016. NATO defense ministers met for a second day on Thursday to discuss Turkeys request to help deal with Europes ongoing migrant crisis and the current situation in Iraq and Syria. (AP Photo/Virginia Mayo)

Secretary of Defense Ash Carter speaks during a Feb. 11, 2016, media conference at NATO headquarters in Brussels. NATO defense ministers met for a second day Thursday to discuss Turkey''s request to help deal with Europe''s ongoing migrant crisis and the current situation in Iraq and Syria.

Photo Credit: Virginia Mayo/AP

Five years of conflict have killed more than a quarter-million people, created Europe's biggest refugee crisis since World War II and allowed the Islamic State to carve out its own territory across parts of Syria and neighboring Iraq.

As Kerry met with the Syria group in Munich, U.S. Defense Secretary Ash Carter was in Brussels to rally fresh support for the fight against the Islamic State group in largely the same territory.

Carter said defense ministers from more than two dozen countries gave a "broad endorsement" of a refined U.S. plan for defeating the Islamic State. After a meeting at NATO headquarters, Carter told reporters that nearly all participants either promised new military commitments or said their governments would consider new contributions. He predicted "tangible gains" in Iraq and Syria by March.

"We will all look back after victory and remember who participated in the fight," he said, appealing to coalition partners to expand and deepen their military contributions.

NATO Secretary-General Jens Stoltenberg said the alliance agreed Thursday to deploy NATO airborne command and control aircraft in order to free up similar U.S. aircraft for the air campaign in Syria and Iraq.

Associated Press writer Nataliya Vasilyeva in Moscow, Jamey Keaten in Geneva, Bassem Mroue in Beirut, Lolita C. Baldor and Bradley Klapper in Washington, Robert Burns in Brussels and Geir Moulson in Munich contributed to this report.