A suspected poison gas attack in Syria has prompted rising tensions over what happens next.
Here are answers to the key questions.
What happened in Syria?
The attack in Douma occurred late on Saturday amid a resumed offensive by Syrian government forces after the collapse of a truce with the Army of Islam rebel group.
Syrian opposition activists and rescuers said poison gas was used on the rebel-held town near the capital, an allegation strongly denied by the Assad government.
The incident has thrust Syria's seven-year-old conflict back to the forefront of international concern and brought the possibility of Western military action against Assad's forces.
How deadly was the attack?
The attack left at least 60 people dead, including children, and more than 1,000 injured, according to a Syrian relief group.
Families were reportedly found suffocated in their homes and shelters, with foam on their mouths.
Reports suggested that hundreds of people, mostly women and children, were brought to medical centres with difficulty breathing, foaming at the mouth, and burning sensations in the eyes.
What has international reaction been?
The use of chemical weapons has been regarded as a line in the sand by the international community.
The UN Secretary General has called for international investigators to have unfettered access after the alleged chemical attack in Syria.
"Any confirmed use of chemical weapons, by any party to the conflict and under any circumstances, is abhorrent and a clear violation of international law," Secretary-General Antonio Guterres said in a statement.
US President Donald Trump said the "horrible attack" will be "met forcefully".
He did not give a time frame for any retaliatory action, but said the US could not stand by as such atrocities take place because "we are able to stop it".
Mr Trump said the US is still investigating the possible involvement of the Iranian and Russian governments.
France said it will retaliate against the regime of the Syrian president if evidence emerges that it was behind the attack, a government spokesman said.
President Bashar al-Assad's government and Russia, his most powerful ally, said there was no evidence that a gas attack had taken place and the claim was bogus.
Russia today said it will propose to the United Nations that international inspectors visit the site of the suspected chemical weapons attack.
It ambassador to the UN, Vassily Nebenzia, earlier warned of the potential consequences to Western intervention in Syria, saying that US attacks on Syria "could lead to grave repercussions".
Have there been attacks like this before?
The attack in Douma comes almost exactly a year after a chemical atrocity in the northern Syrian town of Khan Sheikhoun killed dozens of people.
That attack prompted the US to launch several dozen Tomahawk cruise missiles at a Syrian air base.
When did the conflict in Syria begin?
Protests against Bashar al-Assad's regime began in March 2011 as part of the wider Arab Spring which saw governments overthrown in Libya, Egypt and Tunisia.
Fighting between the army and rebels escalated and by August 2012 the conflict had become a full-blown civil war.
The so-called Islamic State group then took over large swathes of the country.
