Over the past two years about 100,000 people have died in Syria's civil war and millions have fled. Yet Western powers have declined to intervene. Now, in less than a week, that has all changed and Western allies are poised to launch missile strikes.
Almost exactly a year ago US President Barack Obama promised "enormous consequences" if Syrian President Bashar al-Assad crossed a "red line" and used chemical weapons. Last Thursday there were attacks on the area of eastern Ghouta in Damascus. Government and opposition forces have accused each other of unleashing poison gas.
President Obama's national security team hold a meeting. CBS says the meeting included "detailed analysis" of evidence about the chemical attacks that provided "a near air-tight circumstantial case that the Syrian regime was behind it".
French charity Medecins Sans Frontieres says three hospitals it supports in Damascus dealt with 3600 people suffering from "neurotoxic symptoms" over a period of less than three hours on Thursday. Of these, 355 died.
US decides to keep four destroyers in the Mediterranean.
Obama and British Prime Minister David Cameron discuss missile strikes on Syria.
Cameron says Assad's failure to let UN inspectors access the attack site means he has "something to hide".
Media reports say air strikes are likely within a week. Western powers are reported to be prepared to act without UN authority.
The leaders of Britain, France and Germany discuss the crisis. Turkey says it would support action against Syria. Assad says it makes no sense for the regime to use chemical weapons.
Syria allows UN inspectors to visit the site of the attack but a senior Obama Administration official dismisses this as "too late to be credible". A vehicle carrying the inspectors is fired on by snipers but they manage to visit the site. The inspectors visit hospitals, interview witnesses, survivors and doctors and are able to collect some samples.
There are reports that 400 tonnes of arms, paid for by Saudi Arabia, for the rebels have arrived in northern Syria from Turkey.
Secretary of State John Kerry holds a press conference in which he describes the attack as an "obscenity" that "defies any code of morality". He says Syria has been "systemically destroying evidence" by continuing to shell the area that was attacked.
CBS says the Obama Administration will release a declassified report justifying a US military strike in Syria "in a day or two".
CNN says any action "could come as early as mid-week", though it could be later, according to a US official.
Russia reiterates support for the Assad regime and warns that unilateral Western action would be "a very grave violation of international law". President Vladimir Putin tells Cameron there is no evidence yet that the Syrian regime has used chemical weapons. Foreign Minister Sergey Lavrov says reports of the use of chemical weapons must be "thoroughly and professionally investigated" and submitted to the UN. The US State Department says it is cancelling a meeting with Russian diplomats on Syria this week.
Warplanes and military transporters arrive at Britain's Akrotiri airbase on Cyprus, 160km from the Syrian coast.