By Jared Malsin / Gaziantep, Turkey
Updated: February 22, 2016 3:36 PM ET

The U.S., Russia, and other countries have reached an agreement for a cease-fire in Syria, U.S. Secretary of State John Kerry said Monday.

The announcement follows days of lethal violence across Syria. Expectations for a diplomatic breakthrough to end the civil war in Syria remain low, as past proposals for a truce have failed to materialize on the ground. More than 250,000 people have been killed in five years of conflict, and millions have been forced to leave their homes.

“I am gratified to see the final arrangements concluded today for a cessation of hostilities in Syria and call on all parties to accept and fully comply with its terms,” Kerry said in a statement.

The cease-fire is scheduled to go into effect at midnight on Feb. 27 and will not include Islamic State of Iraq and Greater Syria (ISIS) militants or those from Jabhat al-Nusra, the local branch of al-Qaeda.

Kerry’s announcement comes a day after a series of car bombings in Homs and Damascus killed at least 140 people. The killings were a deadly illustration of how jihadists groups — including ISIS and Jabhat al-Nusra — have the ability to derail any cease-fire.

“We are all aware of the significant challenges ahead,” Kerry said. “Over the coming days, we will be working to secure commitments from key parties that they will abide by the terms of this cessation of hostilities and further develop modalities for monitoring and enforcement.”

Kerry’s announcement also follows a lethal escalation in a Russian-backed offensive by the regime of President Bashar Assad, whose forces are trying to reclaim territory lost to rebel groups.

The Russian bombing campaign, primarily in areas held by mainstream rebel groups, has been characterized by attacks on hospitals, schools and other civilian targets. More than 70,000 people fled the offensive in the first 15 days of February alone.

Indirect peace talks in Geneva in late January collapsed following an intensification of Russian air strikes. Opposition groups who agreed in principle to negotiate say they will not participate in talks until past U.N. resolutions on Syria are implemented, calling for an end to attacks on civilians and the lifting of sieges imposed on rebel-held areas.

The most recent proposed cease-fire was announced on Feb. 12 and called for a halt to the violence within one week. The fighting continued as that deadline came and went. As a result, skepticism runs deep among observers and the warring parties in Syria.

“We are accustomed to a norm where, from one international decision to another, the calamity increases,” Zakaria Malahefji, a spokesman for Fastaqim Kama Umirt, a rebel brigade fighting in the city of Aleppo, said in an interview last week.

President Obama spoke on the phone with President Vladimir Putin of Russia on Monday to discuss the cease-fire plan, the White House said. The U.S. provides limited support to some rebel groups opposed to the Assad regime, and also backs Kurdish forces in the international campaign against ISIS.

The agreement calls for a halt to fighting by armed opposition groups, Russian forces, and the Syrian government and “associated forces,” an apparent reference to Iraqi, Iranian and Hizballah forces fighting in support of the regime. The agreement also calls for allowing humanitarian agencies “rapid, safe, unhindered and sustained access” to areas under the parties’ control.

The cease-fire agreement excludes hostilities with “other terrorist organizations as designated by the U.N. Security Council.” Observers of the Syrian conflict say that similar language in past agreements has left open the door to Russian bombing of groups it considers terrorist organizations, a margin of error that could undermine any agreement.

“The agreement on ceasefire in Syria won’t stick unless it specifically tells Russia what targets it can/can’t attack,” said Yury Barmin, an analyst on Russian Middle East policy, writing on Twitter.

Contact us at editors@time.com.

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