(Reuters) - U.N. chemical weapons inspectors in Syria met and took samples from victims of an apparent poison gas attack in a rebel-held suburb of Damascus on Monday after the U.N. team themselves survived a sniper attack on their convoy.
Following are the main events that unfolded after reports of the use of nerve gas on August 21 first emerged.
* AUG. 21 - Syria's opposition accuses government forces of gassing hundreds of people by firing rockets that released deadly fumes over rebel-held Damascus suburbs, killing men, women and children as they slept. If confirmed, it would be the worst chemical weapons attack in 25 years.
- U.N. Security Council holds an emergency meeting and calls for "clarity" on the attack. Western powers demand immediate on-site investigation by U.N. chemical weapons experts. Russia says attack looks like a rebel "provocation" to discredit Syrian President Bashar al-Assad.
* AUG. 22 - United Nations chief and Western powers urge Syria to give U.N. experts immediate access to rebel-held Damascus suburbs where gas attack occurred. Assad's government is silent and U.N. inspectors remain confined to Damascus hotel.
- A U.S. official versed in initial intelligence assessments says the attack appears to be the work of the Assad government, but Washington says will await confirmation of the details, including the perpetrator, before taking any forceful action.
* AUG. 23 - The United States starts repositioning naval forces in the Mediterranean to give President Barack Obama the option for an armed strike on Syria, although officials say he has made no decision on military action. Obama says the attack is of "grave concern" but the ability of Washington to solve the Syrian crisis is "overstated".
- Syrian opposition coalition says samples from victims of the gas attack have been smuggled out of Syria for testing by U.N. experts.
* AUG. 24 - Obama hashes out military options with top advisers and, speaking with British Prime Minister David Cameron, a major ally, agrees any use of poison gas by Assad's forces would merit a "serious response".
- Syrian government reports its soldiers had found chemical weapons in suburban Damascus tunnels used by rebels, evidence, it says, the insurgents were to blame.
- In the most authoritative account yet, medical charity Medecins Sans Frontieres says three hospitals near Damascus reported 355 deaths in the space of three hours, out of about 3,600 people admitted with nerve gas-type symptoms after the reported attacks.
* AUG. 25 - Assad agrees to let United Nations inspect the suspected gas attack site, with a local ceasefire in place to protect inspectors. But a U.S. official says the offer is "too late to be credible". The U.S. remarks appear to signal an increasing likelihood of a military response against Assad.
- France, broadly reflecting views of other Western powers, says it is resolved not to let the chemical attack go unpunished. Russia welcomes decision on U.N. access but warns it will be a "tragic mistake" to jump to conclusions over blame.
* August 26 - U.N. experts cross civil war front lines to reach the nerve gas attack site where they examine victims. En route, the U.N. team's convoy comes under sniper fire, which disables one vehicle, but no one is hurt. Opposition activists blame pro-Assad militiamen for the shooting.
- Underlining diplomatic difficulties in forging international agreement, France says Russia and China would probably veto a U.N. Security Council move to strike Assad. Britain says it would be possible to respond to a chemical weapon attack without the Security Council's backing.
Sources: Reuters reports
(This timeline was refiled to fix date of publication)
(Writing by Mark Heinrich; Editing by Andrew Heavens)
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