UK's May summons Cabinet to discuss Syria military strike

"Final decisions haven't been made yet on that front", Sanders said at the briefing, adding that the president has "not laid out a timetable".

Earlier Thursday, Trump appeared to soften his rhetoric about imminent airstrikes on Syria, a day after warning Russian Federation that missiles "will be coming, nice and new and 'smart.'" In an early morning tweet and later in comments at the White House, Trump worked to cloud the timing of military action and said a final decision had not yet been made.

A similar chemical attack a year ago that killed more than 80 people in northern Syria prompted a limited USA retaliation that targeted an air base from which aircraft involved in the strike likely deployed from.

"Again, to our very foolish leader, do not attack Syria - If you do many very bad things will happen & from that fight the USA gets nothing!"

The ongoing deliberations reflected the conundrum Trump faces as he contemplates wading further into Syria's multi-sided civil war.

Russia, the Syrian government's most important ally in its seven-year-old war with rebels, said it had deployed military police in Douma on Thursday after the town was taken over by government forces.

As Trump has talked about ordering a new military strike on Syria, the regime led by President Bashar Assad has been busy.

"Let us not forget that, ultimately, our efforts must be about ending the awful suffering of the Syrian people", he said.

"We are not surprised by this reckless escalation from a regime like the one in the United States, which has and continues to sponsor terrorism in Syria", the ministry said, adding that statements from Washington lack "wisdom and logic" and endanger global peace and security.

Mattis was expected to voice those concerns in Thursday's meeting at the White House, according to United States officials.

Russia's military has propped up Assad's regime as it wages a multiway war against both the so-called Islamic State and various antigovernment forces.

Mattis said options would be discussed with Trump at a meeting of his National Security Council on Thursday afternoon.

President Trump on Tuesday warned that the USA was prepared to take "forceful" action.

A YouGov poll in The Times conducted this week found that 43 percent of voters oppose strikes in Syria, with 34 percent unsure and only 22 percent supportive.

Trump's Twitter threat, where he said that "nice and new and "smart" missiles were coming for Syria, added another twist to USA conversations with allies in Britain and France.

"But parliament must be involved before any military action is agreed". Opposition activists and rescuers say at least 40 people were killed. Officials said Thursday the trio has yet to reach firm agreement on the scale or timing of a response. Eurocontrol, Europe's main air traffic control agency, said aircraft flying in the eastern Mediterranean should exercise caution due to possible military action against Syria.

Just 22 per cent of the public would support a cruise missile attacks against Syrian military targets, a new poll shows.

British Prime Minister Theresa May was due to hold an emergency cabinet meeting amid speculation she will support USA action against the Syrian regime.

"I think it looks pretty clear that a chlorine weapon was used" on the civilians, said Charles Duelfer, former deputy head of the United Nations inspections team in Iraq, in an interview with NPR.

The remarks by Dmitry Peskov, spokesman for Russian President Vladimir Putin, followed claims by French President Emmanuel Macron of "proof" that Syria used chemical weapons in the attack and a declaration that France will respond at a "time of our choosing".

Those comments go further than USA officials have been willing to in public.

Theresa May is prepared to take action against the Assad regime in Syria without first seeking parliamentary consent, sources have told the BBC.

A European Commission spokeswoman insisted Brussels "has a voice" and the EU "condemns in the strongest terms the use of chemical weapons".