Earlier in the day, Bashar al-Jaafari, Syrian ambassador to the U.S., said in NY that two investigating teams from the OPCW were scheduled to arrive in Syria within the next 24 hours.
In a statement released on Thursday night, a Downing Street spokeswoman said: "The Prime Minister spoke to President Trump about Syria this evening".
May said the aim was to deter the Syrian authorities from further use of chemical weapons and to send a message to the wider world that it was unacceptable to use such weapons.
The Daily Telegraph newspaper said May had ordered British submarines to move within missile range of Syria in readiness for strikes against the Syrian military.
British and French foreign ministers have condemned the use of chemical weapons by anyone and anywhere, a Foreign and Commonwealth Office statement said Monday. It is understood that she was presented with additional intelligence at a meeting of national security advisers yesterday.
"Cabinet agreed that the Assad regime has a track record of the use of chemical weapons and it is highly likely that the regime is responsible for Saturday's attack", it said.
"So there is no practicable alternative to the use of force to degrade and deter the use of chemical weapons by the Syrian Regime".
"Last weekend, up to 75 people were killed, including young children, in a despicable and barbaric attack in Douma".
"There has been no decision to take military action at this point".More news: Davy Russell wins 2018 Grand National aboard Tiger Roll as
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"Russia vows to shoot down any and all missiles fired at Syria", Trump tweeted.
"The Prime Minister said it was a further example of the erosion of worldwide law in relation to the use of chemical weapons, which was deeply concerning to us all".
"I believe that the action taken will have significantly degraded the Syrian regime's ability to use chemical weapons", she said.
Mr Trump provided a fresh twist on the escalating global crisis yesterday, issuing a fresh tweet saying: "Never said when an attack on Syria would take place". She is set to defy calls, including from Jeremy Corbyn, the Labour leader, to follow recent convention and allow MPs a vote, The Times reported.
Russian President Vladimir Putin has denounced a strike on Syria launched by the United States and its allies as an "act of aggression" that will exacerbate humanitarian catastrophe in Syria.
Merkel had said earlier this week that Germany wouldn't join allied military action against Syrian government forces. "But also it's a very, very delicate circumstance and we've got to make this judgement on a very careful, very deliberate, very well thought-through basis".
"We reject any suggestion that she was not entitled to do so", the party's deputy leader said.
Pentagon officials say the attacks targeted the heart of Assad's programs to develop and produce chemical weapons.