International chemical weapons experts will go to the Syrian town of Douma to investigate a suspected poison gas attack, as the US and other Western powers consider military action over the incident.
US President Donald Trump, who had been due to travel to Peru on Friday, cancelled a trip to Latin America to focus on responding to the Syria incident, the White House said. Trump on Monday warned of a quick, forceful response once responsibility for the attack was established.
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France and Britain also discussed with the Trump administration how to respond to the incident. Both stressed that the culprit in the incident still needed to be confirmed.
At least 60 people were killed and more than 1000 injured in Saturday's suspected attack on Douma, then still occupied by rebel forces, according to a Syrian relief group.
Syrian President Bashar al-Assad's government and its ally Russia have said there was no evidence a gas attack had taken place and that the claim was bogus.
Aggravating the volatile situation in the region, Iran, Assad's other main ally, threatened to respond to an air strike on a Syrian military base on Monday that Tehran, Damascus and Moscow have blamed on Israel.
In Syria, thousands of militants and their families arrived in rebel-held parts of the country's northwest after surrendering Douma to government forces.
The Hague-based Organisation for the Prohibition of Chemical Weapons said Syria had been asked to make the necessary arrangements for the deployment of an investigation team.
"The team is preparing to deploy to Syria shortly," it said in a statement on Tuesday.
The mission will aim to determine whether banned munitions were used, but will not assign blame. Doctors and witnesses have said victims showed symptoms of poisoning, possibly by a nerve agent, and reported the smell of chlorine gas.
The Assad government and Russia both urged the OPCW to investigate the allegations of chemical weapons use in Douma, a move apparently aimed at averting any US-led action.
"Syria is keen on co-operating with the OPCW to uncover the truth behind the allegations that some Western sides have been advertising to justify their aggressive intentions," Syria's state news agency SANA said.
Russian Deputy Foreign Minister Mikhail Bogdanov said there was no threat of the situation in Syria resulting in a military clash between Russia and the US. TASS news agency quoted him as saying he believed common sense would prevail.
A European source said European governments were waiting for the OPCW to carry out its investigation and for more solid forensic evidence from the attack to emerge. Any plan by the US and its allies to take military action was likely to be on hold until then, the source said.