President Bashar al-Assad's jets and artillery hit rebel suburbs of the capital again on Sunday in an offensive that residents said began last week when Obama delayed air strikes in the face of opposition from Moscow and his own electorate.
Speaking of the US-Russian deal, Syrian minister Ali Haidar told Moscow's RIA news agency: "These agreements ... are a victory for Syria, achieved thanks to our Russian friends."
Though not close to Assad, Ali was the first Syrian official to react to Saturday's accord in Geneva by US Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov.
Bridging an angry East-West rift over Syria, they agreed to back a nine-month UN programme to destroy Assad's chemical arsenal.
The deal has put off the threat of air strikes Obama made after poison gas killed hundreds of Syrians on August 21, although he has stressed that force remains an option if Assad reneges. US forces remain in position. Russia still opposes military action but now backs possible UN sanctions for non-compliance.
Kerry, visiting Israel, responded to widespread doubts about the feasibility of the "the most far-reaching chemical weapons removal ever" by insisting the plan could work. And he and Obama sought to reassure Israelis the decision to hold fire on Syria does not mean Iran can pursue nuclear weapons with impunity.
Obama embraced the Syria disarmament proposal floated last week by Russian President Vladimir Putin after his plan for US military action hit resistance in Congress. Lawmakers feared an open-ended new entanglement in the Middle East and were troubled by the presence of al Qaeda followers among Assad's opponents.
Obama dismissed critics of his quick-changing tactics on Syria for focusing on "style" not substance. And while thanking Putin for pressing his "client the Assad regime" to disarm, he chided Russia for questioning Assad's guilt over the gas attack.
Responding to concerns, notably in Israel, that a display of American weakness toward Assad could encourage his Iranian backers to develop nuclear weapons, Obama said Tehran's nuclear programme was a "far larger issue" for him than Assad's toxins.
"They shouldn't draw a lesson, that we haven't struck, to think we won't strike Iran," he told ABC television, disclosing he had exchanged letters with Iran's new president. "On the other hand, what they should draw from this lesson is that there is the potential of resolving these issues diplomatically."
Obama had no lack of critics, however, at home and abroad.
John McCain, an opposition Republican senator and supporter of intervention in Syria, said the deal handed Putin the kind of global leverage Moscow had not enjoyed since the Cold War: "It gave Russia a position in the Middle East which they haven't had since the 1970s," he told NBC. "We are now depending on the goodwill of the Russian people ... It's a very big gamble."
Even Obama's Democratic supporters are wary. If Assad scorns his commitments, said Senator Robert Menendez, "We're back to where we started - except Assad has bought more time on the battlefield and has continued to ravage innocent civilians."
Rebels dismiss talks
Syrian national reconciliation minister Ali said Syria welcomed the deal: "They have prevented a war against Syria by denying a pretext to those who wanted to unleash it."
He also echoed Kerry and Lavrov in saying it might help Syrians "sit round one table to settle their internal problems".
But rebels, calling the international focus on poison gas a sideshow, have dismissed talk the arms pact might herald peace talks and said Assad has stepped up an offensive with ordinary weaponry now that the threat of US air strikes has receded.
A spokesman for the opposition Syrian National Coalition repeated that it wanted world powers to prevent Assad's force from using its air force, tanks and artillery on civilian areas.
"Assad is effectively being rewarded for the use of chemical weapons," Shadi Hamid of the Brookings Doha Center wrote in the Atlantic magazine. "Now, he can get away with nearly anything - as long as he sticks to using good old conventional weapons."
International responses to the accord were also guarded. Western governments, wary of Assad and familiar with the years frustrated UN weapons inspectors spent in Saddam Hussein's Iraq, noted the huge technical difficulties in destroying one of the world's biggest chemical arsenals in the midst of civil war.
Iran hailed a US retreat from "extremist behaviour" and welcomed its "rationality". Israel said the deal would be judged on results. China, which like Russia opposes US readiness to use force against sovereign states, was glad of the renewed role for the UN Security Council, where Beijing too has a veto.
The Syrian government has formally told the United Nations it will adhere to a treaty banning chemical weapons. The US-Russian framework agreement calls for the UN to enforce the removal of existing stockpiles by the middle of next year.
Air strikes, shelling and ground attacks on Damascus suburbs on Sunday backed up statements from Assad's supporters and opponents that he is back on the offensive after a lull in which his troops took up defensive positions, expecting US strikes.
"It's a clever proposal from Russia to prevent the attacks," said an Assad supporter from the port city of Tartous.
An opposition activist in Damascus echoed disappointment among rebel leaders: "Helping Syrians would mean stopping the bloodshed," he said. Poison gas is estimated to have killed only hundreds of the more than 100,000 dead in a war that has also forced a third of the population to flee their homes since 2011.
Russia says it is not specifically supporting Assad - though it has provided much of his weaponry. Its concern, it says, is to prevent Assad's Western and Arab enemies from imposing their will on a sovereign state. And Moscow, like Assad, highlights the role of al Qaeda-linked Islamists among the rebel forces.
Their presence, and divisions among Assad's opponents in a war that has inflamed sectarian passions across the region, have tempered Western support. Al Qaeda leader Ayman al-Zawahri urged followers on Sunday not to cooperate with other Syrian rebels.
The opposition Syrian National Coalition elected a moderate Islamist on Saturday as prime minister of an exile government - a move some members said was opposed by Western powers who want to see an international peace conference bring the warring sides together to produce a compromise transitional administration.
Previous attempts to revive peace efforts begun last year at Geneva have foundered on the bitter hostilities among Syrians.
Newly elected Coalition leader Ahmad Tumeh, a moderate Islamist, told Reuters he wanted to form a government that could bring order to rebel-held areas and to challenge al Qaeda there.
Assad has just a week to begin complying with the US-Russian deal by handing over a full account of his chemical arsenal. He must allow UN-backed inspectors from the Hague-based Organisation for the Prohibition of Chemical Weapons (OPCW) to complete their initial on-site checks by November.
Under the Geneva pact, the United States and Russia will back a UN enforcement mechanism. But its terms are not yet set. Russia is unlikely to support the military option that Obama said he was still ready to use: "If diplomacy fails, the United States remains prepared to act," he said on Saturday.
Assad told Russian state television last week that his cooperation was dependent on an end to such threats and US support for rebel fighters. But it seems likely that Moscow can prevail on him to comply, at least initially, with a deal in which Putin has invested considerable personal prestige.
While Lavrov stressed in Geneva that the pact did not include any automatic use of force in the event of Syria's failure to comply, Western leaders said only the credible prospect of being bombed had persuaded Assad to agree to give up weaponry which he had long denied ever having, let alone using.
Kerry and Lavrov plan to meet the UN envoy on Syria at the end of the month to review progress toward peace talks. Lavrov spoke of an international peace conference as early as October.
Fighting on the ground in a country divided between rebel and government forces shows little sign of slowing its descent into atrocity, with 1,000 people dying in any typical week.
But in government-held parts of Damascus schools reopened on Sunday after the summer break and traffic was heavy - further signs the authorities see the US threat has passed for now. Many schools had been used earlier in the month to house troops evacuated from barracks that might have become US targets.
Lavrov and Kerry, whose personal rapport played a part in breaking some of the Cold War-era ice over Syria, both welcomed their agreement as a victory for diplomacy.
But the OPCW has never moved weapons abroad before, due to the risk, and has never worked in a war zone.