RUSSIA’S announcement that Syrian warplanes will stop flying over some of the country’s bloodiest battlefields should be cause for joy. No accurate figure exists for the number of people killed during the war, but monitoring groups estimate that 470,000 have died, the vast majority of them civilians. What is certain, however, is that the Syrian air force, with the help of Russia and Iran, has killed most of these people. Its helicopters and warplanes have dropped bombs, missiles and gas on schools, hospitals and homes. Ending the slaughter means first grounding the regime’s air force.

Under the terms of a deal signed by Russia, Iran and Turkey at talks in Kazakhstan on May 4th, this is what is supposed to happen. All operations, including Syrian military flights, will supposedly stop in four “de-escalation zones” within the country where opposition fighters still hold considerable territory. If all sides abide by the deal, then these areas will become safe zones that could, at some stage, be policed by troops from Russia and Turkey. Russian news outlets speculated that troops from Brazil and India may also play a role in peacekeeping. Donald Trump is reported to have approved the agreement in a call with the Russian president, Vladimir Putin.

The ambitious plan is the latest in a series of attempts to put an end to the six-year war. Details on exactly how it will work on the ground are thin and there are a number of possible spoilers. Key to the plan’s success will be the Syrian government’s commitment to its terms. Backed by its allies Russia and Iran, the regime has repeatedly vowed to continue fighting until it controls the entire country. In trying, it has often acted against the interests of both its main sponsors.

The rebels are justifiably suspicious of the deal, pointing out that Russia has failed to rein in its unruly partner in the past. They are also deeply sceptical about the role of Iran, which they accuse of deliberately stoking sectarian hatred during the war (rebel representatives walked out of talks on Wednesday in protest at Iran’s role as a signatory and guarantor of the latest deal). This mistrust has seen previous ceasefire agreements collapse within weeks, with both sides accusing each other of violating their terms.

Little has changed to make it any more likely that this latest effort will succeed where the others have failed. Under the new deal, Russia, Iran and the regime are still allowed to target jihadists linked to al-Qaeda, who fight side by side with other rebel factions in some parts of the country, including within the designated safe areas. The regime has in the past used this co-operation to justify breaking ceasefires and bombing rebel positions. In Idlib, which is supposed to fall inside one of the four safe zones, al-Qaeda-linked factions now dominate an alliance of rebel groups that controls most of the province. It is unlikely that the regime will stop its bombing campaign there. Nor is it likely that the rebel alliance will stop attacking the regime. Both sides will accuse the other of violating the ceasefire.

Like Idlib, many of the areas where the conflict will supposedly be paused as part of the deal have seen an escalation in fighting in recent months. Government forces and pro-regime militias have tightened the sieges of Eastern Ghouta, a densely populated rebel-held suburb of Damascus, and the rebel redoubt north of the city of Homs. The deal will also cover an area in the south, along the Jordanian border, where American-backed rebel forces have made gains against both Islamic State and government forces since the start of the year. “As of the sixth of this month all military operations will be ceased,” the head of the Russian delegation to the talks in Kazakhstan, Alexander Lavrentyev, said. “All Syrian flights over these areas will cease.” If this happens, then separate talks in Geneva aimed at finding a lasting political solution to the war may finally move forward. The chances of this happening, however, are slim.