JERUSALEM — Secretary of State John Kerry announced on Sunday an agreement with Russia for an imminent, if “provisional,” partial truce in Syria, saying it largely awaited a conversation between President Obama and President Vladimir V. Putin to work out final details.

Mr. Kerry’s announcement came at the end of a day of meetings in Jordan. Just hours after he spoke, multiple suicide attacks claimed by the Islamic State ripped through the central city of Homs and a suburb of the capital, Damascus, killing more than 100 people and wounding dozens. One of the attacks was in an area of Homs where many Alawites, the sect of Syria’s president, Bashar al-Assad, live and work. It was the target last month of another bombing claimed by the Islamic State.

It was the second time in 10 days that Mr. Kerry had announced a “cessation of hostilities” that would go into effect in days — a phrase that was carefully chosen to avoid all of the connotations of a full cease-fire. The first occasion was in Munich in the early-morning hours of Feb. 12. He said at the time it would go into effect a week later, which would have been last Friday. The interim time, he said, would be used to work out the “modalities” of the cease-fire, with the Russians responsible for getting the forces of Iran and Mr. Assad on board, and the United States for getting the agreement of the various disputatious opposition groups.

That deadline passed with no changes on the ground, except for the beginnings of deliveries of relief aid to five besieged Syrian towns. State Department officials later said the deadline was more a target to keep momentum going rather than a hard deadline, but in the days leading up to it, Mr. Kerry spoke frequently with Sergey V. Lavrov, the Russian foreign minister. The two men are supposed to be the co-chairmen of a task force to put in effect the cessation of hostilities.