The prime minister will summon the cabinet on Thursday to discuss the government’s response to the suspected chemical weapons attack in Syria.
Ministers will consider the options for backing military action threatened by the United States and its allies.
Theresa May is prepared to take action against the Assad regime in Syria without first seeking parliamentary consent, sources have told the BBC.
The allies wants to prevent a repeat of an apparent chemical attack in Douma.
Mrs May has said “all the indications” are that the Syrian regime of president Bashar al-Assad, which denies mounting a chemical attack, was responsible.
If the cabinet approves UK involvement in military action, that would open the way for British forces to join an operation against Syrian targets that US President Donald Trump has said in a tweet “will be coming”.
Mrs May is reluctant to ask US President Donald Trump to hold off any action until she has the opportunity to consult MPs, the BBC understands from well-placed sources.
MPs are due return to Westminster from the Easter recess on Monday,
Labour’s Jeremy Corbyn has warned that bombing could escalate the situation in Syria.
Mrs May is still yet to unequivocally point the finger of blame at the Assad government, the BBC’s deputy political editor John Pienaar said, but she has spoken of the need for action “if” the regime is found to bear responsibility.
The strong assumption in Downing Street and Whitehall is the attack will be attributed to the forces of President Bashar al-Assad and action is thought likely to follow within days, he added.
Mrs May earlier described the use of chemical weapons as a “humanitarian catastrophe” that “cannot go unchallenged”.
She did not comment on Donald Trump’s tweeted warning Russia to “get ready” for missiles being fired at its ally Syria.
By the BBC’s Deputy Political Editor John Pienaar
The prime minister’s instinct is to chew carefully on the decision of whether and how Britain should support action in response to the apparent chemical attack in Syria. She still speaks of the need to act “if” not “as” the Assad regime is responsible.
But the uncomfortable truth is the form of action is beyond her control.
Labour leader Jeremy Corbyn told the BBC that Parliament “should always be given a say on any military action”.
“We don’t want bombardment which leads to escalation and a hot war between the US and Russia over the skies of Syria,” he added.
Lib Dem leader Sir Vince Cable did not rule out backing military but he said Parliament would have to give its approval with conditions.
Medical sources say dozens of people were killed, including children, during the alleged toxic bombing of the formerly rebel-held town of Douma, in the Eastern Ghouta region.
Russia has described the reports of the chemical attack as a “provocation” designed to justify Western intervention against the Syrian regime.
Mrs May described the alleged chemical attack as a “shocking, barbaric act” and said she was “appalled but not surprised” at Russia, which vetoed a US-drafted UN resolution proposing a new inquiry to establish who was to blame.
The UK and its allies were looking at ways to “prevent and deter” the use of chemical weapons, she added.