Theresa May joined the US president, Donald Trump, and the French leader, Emmanuel Macron, on Tuesday in warning that they would respond to the Syrian gas attack in order to uphold the global ban on the use of chemical weapons.

In separate phone calls, the three allies agreed that the international community should work closely together to make sure that the regime, and its backers, were held to account.



The prime minister is facing mounting pressure from senior Conservative MPs to support US-led airstrikes against the regime of Syrian president, Bashar al-Assad, after the suspected chemical attack in Douma that killed dozens of people.



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Earlier, she chaired a meeting of senior intelligence officials and ministers at her so-called “war cabinet”, the National Security Council, to discuss the crisis, which is pushing the US and Russia closer to a direct confrontation over the Middle East.



A Downing Street spokesman said of the calls: “They agreed that reports of a chemical weapons attack in Syria were utterly reprehensible and, if confirmed, represented further evidence of the Assad regime’s appalling cruelty against its own people and total disregard for its legal obligations not to use these weapons.

“They agreed that the international community needed to respond to uphold the worldwide prohibition on the use of chemical weapons. They agreed they would continue working closely together and with international partners to ensure that those responsible were held to account.”

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UK government sources have expressed concern that if Britain were to take part in any action taken to punish the Assad, regime it would have to be approved by parliament. David Cameron suffered a serious blow to his credibility when he lost a historic Commons vote in 2013 over launching airstrikes.

However, Tom Tugendhat, the chair of the foreign affairs select committee, said: “Striking Syria’s stockpiles of chemical weapons would degrade their ability to commit further war crimes and could be done together with allies. It would not require a vote in Parliament.”

A White House spokesman said: “Both leaders condemned Syrian president Assad’s vicious disregard for human life. The president and prime minister agreed not to allow the use of chemical weapons to continue.”



May said Britain was working urgently with allies and partners to assess what had happened on the ground in Douma on Saturday, while deflecting questions over whether the UK would take part in a joint international response to the atrocity.



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The prime minister condemned the “brutality” of the attack, adding: “Of course we’ll be talking about this issue, including the discussions that have been taking place at the security council of the United Nations.”



It came as the war of words between the US and Russia escalated after Trump said a decision was imminent on a response to the attack on the outskirts of Damascus, while Russia said any western military response would have “grave repercussions”.

May has said the Assad regime and its Russian backers must be held to account if found responsible for the poison gas attack on the rebel-held town of Douma that killed at least 42 people.



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She did not rule out joining international military action against the Syrian regime on a trip to Scandinavia on Monday, but refused to elaborate on the range of options that could be available to the government.



But she added: “We are working urgently with our allies to asses what has happened. But, we are also working with our allies on any action that is necessary.”



Boris Johnson, the UK foreign secretary, has said that “a full range of options should be on the table” for the international community in response to the attack. This is understood to include airstrikes against military targets.

A former minister, Nick Boles, said May had his “strong support” if she decided to join the US and France in taking action against the Syrian regime. “Parliament should have a chance to debate the crisis early next week, but this should not become an excuse for inaction or delay,” he said.

The former attorney general Dominic Grieve added: “In view of the enormity of what has been done, if there is a way of preventing its recurrence by the limited use of force, that is one thing, and I would be supportive.” But he warned that a wider campaign against Syria would need the backing of Parliament.

However, not all Tory backbenchers were convinced. Bob Seely, a member of the foreign affairs select committee who backed airstrikes against Syria in 2013, said: “If we bomb now, I don’t think we’re going to achieve anything, but merely make a cold war with Russia into a potential hot one.”