An alleged Syrian chemical attack on one-time rebel-held Douma has prompted outraged Western powers to order retaliatory strikes and Russia to warn against a dangerous escalation of tensions.

Here is a recap of events:

'Toxic gas'

On April 7, the Syrian American Medical Society (SAMS) and Syria's White Helmets jointly say more than 40 people have died in a “poisonous chlorine gas” in Douma, the last opposition-held town in Eastern Ghouta near the capital.

Blaming the government, they say there are “more than 500 cases” of people with “symptoms indicative of exposure to a chemical agent”.

The Syrian Observatory for Human Rights, a Britain-based monitor, does not confirm a chemical attack.

However, it reports at least 70 cases of respiratory difficulties among civilians after regime air strikes, saying 11 people had died.

The regime and its key ally Russia deny any chemical attack.

'Big price to pay'

The following day, US President Donald Trump tweets a warning aimed at Syrian President Bashar al-Assad and his allies that there will be a “big price to pay” after a “mindless CHEMICAL attack”.

He hits out at Russia and Iran for backing “Animal Assad”.

Moscow warns Washington against carrying out a “military intervention on fabricated pretexts” which “could have the most dire consequences”.

Military alert

On April 9, US ambassador at the UN, Nikki Haley, says Washington is determined to “see the monster who dropped chemical weapons on the Syrian people is held to account”.

The USS Donald Cook — a guided-missile destroyer — leaves Cyprus, moving within easy striking range of Syria.

On April 10, the Syrian army puts its airports and military bases on alert, the Observatory reports.

The global chemical weapons watchdog, the Organisation for the Prohibition of Chemical Weapons, announces a fact-finding mission to Douma.

At the UN, Russia vetoes a US-drafted Security Council resolution that would have set up an investigation into chemical weapons use in Syria.

Missiles 'coming'

On April 11, Trump tells Moscow to be prepared for a retaliatory missile strike. “Get ready Russia, because they will be coming, nice and new and smart!” he says on Twitter.

But White House says later that no final decisions on a response have been made although “all options are on the table”.

The Russian defence ministry dismisses footage of attack victims as “yet another fake”, and a staged “provocation” to justify Western intervention.

Ghouta retaken

On April 12, Russia announces that remaining fighters in Douma had given up their heavy weapons, meaning the whole of Ghouta was all-but under pro-regime control.

“Of course, the chemical attack is what pushed us to agree” to a withdrawal from Douma, a top rebel official tells AFP.

President Emmanuel Macron says France has “proof” that the Syrian regime had used chemical weapons and would respond “at a time of our choosing”.

Russia's UN ambassador says US-led strikes could lead to a confrontation between the world's two preeminent nuclear powers.

“The immediate priority is to avert the danger of war,” says Vassily Nebenzia.

Russian President Vladimir Putin calls Macron on April 13 to warn against any “dangerous actions” with “unpredictable consequences”, the Kremlin says.

'Staged by London'

Russian Foreign Minister Sergei Lavrov says Moscow has “irrefutable” evidence the alleged chemical attack was staged as part of a “Russophobic campaign” led by the secret services of a foreign power.

The Russian military points the finger at London.

At a meeting of the Security Council, UN chief Antonio Guterres says the spiralling tensions could lead to a “full-blown military escalation” and urges the body to “act responsibly”.

Fact-finding experts from the global chemical weapons watchdog say they will start work on the ground in Douma on April 14.

US, France and UK strike bases, chemical research centres in Syria

President Donald Trump announces on April 13 that the United States, France and Britain have launched military strikes in Syria to punish President Bashar Assad for a suspected chemical attack against civilians and to deter him from doing it again. Trump says the US is prepared to exert sustained pressure on Assad.