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

Kerry’s announcement came at the end of a day of meetings in Amman, Jordan.

Just hours after he spoke, multiple suicide attacks claimed by the Islamic State ripped through the central city of Homs and in a suburb of the capital, Damascus, killing more than 100 and wounding dozens. Most of the victims were civilians.

One of the attacks was in an area of Homs where many Alawites, the sect of Syria’s president, Bashar Assad, live and work. The attackers blew up two car bombs in a neighborhood home, killing at least 46, according to the Syrian Observatory for Human Rights, which tracks the conflict from Britain through a network of contacts in Syria.

At least three blasts struck the Damascus suburb of Sayeda Zeinab, home to an important Shi’ite shrine, killing more than 60 people and wounding 180, according to the Observatory.

Some reports suggested the bombers had detonated a car bomb before blowing themselves up, causing the multiple blasts.

Elsewhere Sunday, government forces backed by Russian airstrikes pushed their offensive against the rebels in what many analysts believe is an effort to solidify gains before any peace talks begin.

It was the second time in 10 days that Kerry had announced a “cessation of hostilities’’ that would go into effect in days — a phrase that was carefully chosen to avoid all 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 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 date was intended to keep momentum going rather than a hard deadline, but in the days leading up to it Kerry spoke frequently with Sergey Lavrov, the Russian foreign minister.

In Amman on Sunday, Kerry was vague about the timing, perhaps cautious about announcing another deadline that may not hold up.

“We have reached a provisional agreement in principle on the terms of a cessation of hostilities that could begin in the coming days,’’ he said. “It is not yet done, and I anticipate that our presidents — President Obama and President Putin — may well speak somewhere in the next days or so, in order to try to complete this task.’’

Kerry is known as an eternal optimist when it comes to negotiations: That paid off in his relentless pursuit of a nuclear deal with Iran, and again with the global climate change pact reached in Paris at the end of last year. It failed in his first big project as secretary of state, an effort to revive the Israel-Palestinian negotiating process.

But Syria remains his biggest test, a humanitarian disaster than many in the Obama administration concede, at least in private, they responded to insufficiently.

Kerry seemed testy about his critics on Sunday, telling reporters: “Now, a lot of cynics have criticized our diplomatic efforts. But I want to point out very clearly they have not offered a realistic alternative that actually decreases the bloodshed and ends the conflict.

“Nobody would like to see our diplomatic efforts move more quickly than I would,’’ he said. “But the truth is we are, in fact, making progress, even as I stand here today. There is aid now getting through.’’

Part of the complication is that the cease-fire would exempt attacks on the Islamic State and on Al Nusra, both recognized as terrorist organizations by the United Nations.

Russia maintains that because there are Al Nusra elements remaining in Aleppo, where it has conducted a brutal air campaign, the bombing of that city can continue. Kerry and White House officials see that as an excuse to bomb the opposition groups fighting Assad. An opposition spokesman, Riad Hijab, said there was preliminary support for a truce, provided Iran, Russia, and their militias stop fighting.

In a separate development Sunday, a prominent member of the Saudi royal family, Prince Turki al-Faisal, said the kingdom’s offer to send troops to Syria to fight extremist groups reflects growing unease over the ability of US-led airstrikes alone to defeat the Islamic State group and end the civil war.

Speaking at a luncheon in Abu Dhabi, Faisal said the kingdom does not expect the US-led coalition, of which Saudi Arabia is a member, will succeed unless there is a ground intervention. “There has to be concrete action on the ground to put a stop to the killing,’’ he said.

Speaking earlier at a press conference, he said Muslim countries need to take the lead in fighting terrorism, but Saudi Arabia has made clear that its willingness to send special forces to Syria is contingent on the United States leading the ground effort.