This week’s eleventh-hour Russian initiative interrupted a Western march to war, persuading President Barack Obama to put on hold a plan for military strikes to punish Assad for a poison gas attack that killed hundreds of civilians on August 21.

Syria, which denies it was behind that attack, has agreed to Moscow’s proposal that it give up its chemical weapons stocks, averting what would have been the first direct Western intervention in a war that has killed more than 100,000 people.

A version of the Russian plan leaked to the newspaper described four stages: Syria would join the world body that enforces a ban on chemical weapons, declare its production and storage sites, invite inspectors and then decide with the inspectors how and by whom stockpiles would be destroyed.

In the past Syria had not confirmed that it held chemical weapons. It was not a party to treaties that banned their possession and required disclosure, although it was bound by the Geneva Conventions that prohibit their use in warfare.

While the diplomats gathered in Switzerland, civil war ground on relentlessly in Syria itself. Activists said warplanes bombed one of the main hospitals serving rebel-held territory in the north of the country, killing at least 11 civilians including two doctors.

Video footage showed the limp body of a young child being carried out of the hospital by a man. Another boy lay on the floor, blood on his head and dust covering his body.

Rebels say the US climb-down from strikes - and the shift in emphasis in Western diplomacy from demanding Assad’s removal from power to the narrower aim of forcing him to relinquish chemical weapons - emboldened his forces to take the offensive.

Assad’s opponents are also accused of atrocities. An anti-Assad monitoring group, the Syrian Observatory for Human Rights, said on Thursday that Sunni Muslim Islamist rebels had killed 22 members of Assad’s Alawite minority sect in a massacre after storming a village east of the central city of Homs.

Looking back over past months, a report by a UN commission documented eight mass killings, attributing all but one to Assad’s forces, including two massacres in May that killed up to 450 civilians.

The US official, briefing the media on condition of anonymity ahead of Kerry’s talks with Lavrov, said the aim of the talks in Geneva was “to see if there’s reality here, or not” in the Russian proposal. Kerry and a contingent of experts plan to hold at least two days of talks with the Russians.

Russia’s President Vladimir Putin, long cast as a villain by Western leaders for supplying Assad with arms and blocking Security Council efforts to dislodge him, took his case to the American public, penning an op-ed piece in the in which he argued against military strikes.

Putin argued that intervention against Assad would further the aims of al-Qaeda fighters among the Syrian leader’s enemies.

There were “few champions of democracy” in Syria, he wrote, “but there are more than enough Qaeda fighters and extremists of all types battling the government.”

US intervention would “increase violence and unleash a new wave of terrorism,” Putin argued. “It is alarming that military intervention in internal conflicts in foreign countries has become commonplace for the United States. Is it in America’s long-term interest? I doubt it.”

US officials said they hoped Kerry and Lavrov could agree on a blueprint for Syrian disarmament whose main points would be adopted in a UN Security Council resolution.

The five permanent veto-wielding powers of the UN Security Council met in New York on Wednesday. Britain, France and the United States want the Security Council to include tough consequences if Assad is seen to renege. An initial French draft called for an ultimatum to Assad’s government to give up its chemical arsenal or face punitive measures.

The Russian initiative offers Obama a way out of a threat to use force which is deeply unpopular among Americans exhausted by the 2003 invasion of Iraq and still embroiled in the longest war in US history in Afghanistan.

Obama had asked Congress for authorisation for strikes and faced a tough fight persuading sceptical lawmakers in both parties of the case. That vote is now on hold.

The sudden pull-back from the brink is a blow for rebels who have listened to Obama and other Western leaders declare in strong terms for two years that Assad must be removed from power, while wavering over whether to use force to push him out.

Turkish Prime Minister Tayyip Erdogan, one of the main opponents of Assad within the region, dismissed the Russian plan.

“The Assad regime has not lived up to any of its pledges. It has won more time for new massacres and continues to do so,” he said. “We are doubtful that the promises regarding chemical weapons will be met.”

The rebels are armed by Saudi Arabia and Qatar, which are expected to continue to send weapons and funds although the odds of victory are longer without Western action.

Rebels have long pleaded with the West for advanced weapons to counter Assad’s firepower. Obama promised unspecified military aid in June; Washington has trained rebel units but has not delivered arms.

General Salim Idris, the head of the Free Syrian Army that is the acceptable face of the rebels in the West, said in a US radio interview his forces had been poised to launch coordinated attacks with US missile strikes.

“We were and are still waiting for these strikes,” he said. “We are waiting and still waiting to receive weapons and ammunition, and we told our friends in the United States we hope that you will support us.”

Enthusiasm for the rebel cause has diminished in the West because of the growing power of al-Qaeda-linked fighters among Assad’s foes. Mainstream opposition leaders say the West’s tepid support is to blame for the rise of extremists.

Assad’s forces have pressed on with offensives in Damascus suburbs, including those that were the targets of the August 21 gas attack, in the days since the Russian initiative emerged.

Kerry is accompanied by a large retinue of experts in anticipation of detailed talks on how to turn the Russian offer into a concrete plan along the lines of disarmament accords between Washington and Moscow since the days of the cold war.

“What we are seeking ... is the rapid removal of the repeated use of chemical weapons by the regime. And that means a rapid beginning to international control” over the stockpiles, said a second senior official travelling with Kerry.

The US delegation will present the Russians with U.S. spy services’ assessment of the scope of Syria’s chemical weapons infrastructure, believed to be among the world’s largest, said the first US official.

Inspecting, securing and neutralising chemical weapons in the midst of an ongoing civil war that has killed over 100,000 people will be a stiff challenge. “It is doable, but difficult and complicated,” the first US official said.