Syrians inspect damage after a reported government airstrike April 7 in the rebel-held town of Douma, on the outskirts of Damascus. The town is part of Eastern Ghouta, one of four areas designated as safe zones in an agreement announced Thursday. (Abd Doumany/Agence France-Presse via Getty Images)

Russia, Iran and Turkey said Thursday that they have agreed to create “de-escalation zones” across four areas in Syria, renewing diplomatic ­efforts to bring warring parties in the country to heel after six years of fighting. 

Meeting in the Kazakh capital, Astana, the three powers said the cease-fire deal would come into force Saturday and would apply to both government and rebel forces in the designated areas, where the Islamic State does not hold large swaths of territory.

The agreement, signed by all three guarantor countries, said that the zones would be demarcated by checkpoints on the ground and that “unarmed ­civilians” would be able to move freely between government- and ­opposition-held territory. Checkpoints would be overseen by the three guarantors but could, “if necessary,” be manned by unspecified “third parties,” it said.

But it was unclear how the deal differed from several previous failed cease-fires in which the Syrian air force continued to bomb rebel-held areas. The agreement said “the parties agreed to take all necessary measures to continue the fight” against designated terrorist groups “within and outside” the zones.

A hospital was badly damaged in an airstrike in Eastern Ghouta on May 1. (Sameer Al-Doumy/Agence France-Presse via Getty Images)

Although Russia and Iran exert influence over Syrian President Bashar al-Assad and Turkey is an important backer of the rebels, there were few early signs that either side was committed to the deal. 

In Astana, where the three international powers are overseeing peace talks, the announcement caused a ruckus in the rebel delegation, with one top commander shouting, “See you on the battlefield!”

The Syrian Observatory for Human Rights, a monitoring group based in Britain, also said that the Syrian air force stepped up strikes in the proposed de-escalation zones after their locations were revealed in a Russian draft proposal Wednesday. 

The State Department, noting that it was “not a direct participant” in the talks, although it sent an official to observe, said it supported “any effort that can genuinely de-escalate the violence in Syria,” ensure humanitarian aid and promote a political resolution to the conflict.

But the statement, by spokeswoman Heather Nauert, said that “we continue to have concerns” about the agreement, “including the involvement of Iran as a so-called ‘guarantor.’ ” It added: “Iran’s activities in Syria have only contributed to the violence, not stopped it, and Iran’s unquestioning support for the Assad regime has perpetuated the misery of ordinary Syrians.”

The cease-fire agreement excludes attacks on al-Qaeda’s ­Syrian affiliate — the group known formerly as Jabhat al-
Nusra and now as Jabhat Fatah al-Sham — and the Islamic State. In earlier truces agreed to between the Obama administration and Russia, that exclusion led both Russia and Syria to continue bombing rebel and civilian areas, arguing that they were targeting “terrorists.”

“In light of the failures of past agreements,” Nauert’s statement said, “we have reason to be cautious. We expect the regime to stop all attacks on civilians and opposition forces, something they have never done. We expect Russia to ensure regime compliance.”

The White House said this week that President Trump and Russian President Vladi­mir Putin discussed “safe, or de-escalation, zones” in a Tuesday phone call. But the Trump administration has not specified publicly what it is willing to support or how.

At least half a million people are estimated to have been killed in Syria’s war, and half its population displaced.

According to the Kazakhstan agreement, the proposed safe zones will cover four areas: the northern province of Idlib, where almost a million displaced people are packed among rebel forces dominated by al-Qaeda, and some portions of adjoining provinces; Eastern Ghouta, a besieged area on the outskirts of Damascus that is the last remaining threat to Assad’s hold on the capital; a besieged district of the government-controlled city of Homs, 100 miles north of Damascus; and a swath of Syria’s southern border with Jordan where the United States is supporting rebel forces against Islamic State militants.

Except for the stated exceptions for “terrorists,” it said that “hostilities between” Assad’s forces and those rebel groups that sign on, “with the use of any kinds of weapons, including aerial assets, shall be ceased.”

Maps of the delineated cease-fire areas are expected to be agreed to by June 4, along with plans to deliver humanitarian aid and ensure the safe return of civilians who fled.

The United Nations’ Syria envoy, Staffan de Mistura, hailed the announcement as a “step in the right direction” toward a broader truce. But experts suggested its guarantors might be using its provisions to secure their own interests in Syria. 

“Russia opposed no-fly zones at the time when it was still busy, along with Iran, assisting Assad’s forces in, first, stabilizing the front and then rolling back the gains made by the opposition forces,” said Simon Saradzhyan, the founding director of the Russia Matters Project at Harvard’s Belfer Center for Science and International Affairs.

With the rebels all but defeated, Saradzhyan argued, Russia is now ready to support a diplomatic solution with international backing. 

Turkey has also backed safe zones in the past, albeit in different areas along its southern border with Syria, viewing them as a way to block Kurdish ambitions in that region.  

While Washington is backing the Kurdish People’s Protection Units (YPG) as an essential partner in the fight to defeat the Islamic State in Syria, Turkey is locked in battle with the group’s Turkish affiliate, the Kurdistan Workers’ Party (PKK), which the United States also lists as a terrorist organization. 

The U.S.-Kurdish alliance has been a major thorn in the side of the U.S. relationship with Turkey and is likely to be a central agenda item when Turkish President Recep Tayyip Erdogan visits Trump in Washington on May 16.

“Every side in this fight wants something,” said one rebel official, speaking on the condition of anonymity because he was not authorized to comment publicly. “The foreign powers aren’t doing this for altruism.”

DeYoung reported from Washington. Zakaria Zakaria in Istanbul and Andrew Roth in Moscow contributed to this report.