Britain's opposition Labour Party leader has criticised Prime Minister Theresa May for "waiting for instructions" from President Trump on Syria.
Jeremy Corbyn, a veteran anti-war campaigner, said the UK should press for an independent UN-led investigation into the chemical attack in Syria rather than following the lead of the United States.
"The government appears to be waiting for instructions from President Donald Trump on how to proceed," Mr Corbyn said in a statement.
"Britain should press for an independent UN-led investigation of last weekend's horrific chemical weapons attack so that those responsible can be held to account."
Mrs May on Thursday won backing from her senior ministers to take unspecified action with the US and France to deter further use of chemical weapons by Syria.
Mr Corbyn has said parliament should be consulted before any military action. A YouGov poll showed just one in five members of the public support a strike on Syria.
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Mrs May has said that Russia's veto at the Security Council of a vote to create a new inquiry on chemical attacks meant the UN could have no role in investigations.
Her office said that she had talked with Mr Trump by telephone on Thursday evening to discuss Syria.
In the call, the two leaders had agreed that the regime of Syrian President Bashar Al Assad "had established a pattern of dangerous behaviour in relation to the use of chemical weapons", Downing Street said.
Mrs May and Mr Trump had also "agreed it was vital that the use of chemical weapons did not go unchallenged, and on the need to deter the further use of chemical weapons by the Assad regime.
"They agreed to keep working closely together on the international response," the statement concluded.
Mr Trump is considering his military options in Syria after Saturday's chemical attack against the rebel-held town of Douma.
His French counterpart Emmanuel Macron said he was in daily contact with Mr Trump, stating France has evidence that Assad's regime was behind the attack.
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Read: French President says they have "proof" of chemical weapons being used
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But British involvement in further military intervention is controversial at home, in a country still haunted by its role in the US-led invasion of Iraq.
The government said it is "highly likely" that Assad is responsible for the Douma attack, with ministers agreeing "it was vital that the use of chemical weapons did not go unchallenged".
But rival politicians and some Conservative colleagues have called for a parliamentary vote before any British involvement.
Mr Corbyn said it is "vital that parliament has the chance to debate and decide in advance" of any military action, which he warned "risks a dangerous escalation of the conflict".
Mr Corbyn has also evoked memories of the Iraq War, when lawmakers approved joining in the face of strong public opposition.
A YouGov poll in The Times conducted this week found that 43 percent of British voters oppose strikes in Syria, with 34 percent unsure and only 22 percent supportive.