Donald Trump and Theresa May have agreed in a phone call that the use of chemical weapons in the Syrian civil war must not go “unchallenged”, ahead of expected military action against the country’s government.

They spoke having both just held meetings with senior officials and used the conversation to draw attention to their joint view that the regime of Bashar al-Assad is to blame for the recent chemical attack in the town of Douma.

But with British, American and French forces either moving into, or already in position, Jeremy Corbyn claimed Ms May was “waiting for instructions from Donald Trump” in her approach to Syria.

As the West stood on the brink of an escalated Middle Eastern conflict today, Mr Trump was due to speak to French President Emmanuel Macron while Russia called for a new meeting of the UN Security Council.

After the phone call on Friday, a Downing Street spokesperson said: “The prime minister spoke to President Trump about Syria this evening.

“They agreed that the Assad regime had established a pattern of dangerous behaviour in relation to the use of chemical weapons.

“They 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.”

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It is possible that an attack could come this weekend, with British attack submarines said to be on standby in the Mediterranean Sea, while RAF fighter jets based in Cyprus could also be used.

The US nuclear-powered aircraft carrier, the USS Harry Truman, could be utilised having set sail from Virginia this week, on its way to form part of the largest US task force since the Iraq War.

They 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 <p>Downing Street statement on phone call between May and Trump</p>

While Mr Trump said no final decision had been taken on military action yet, the UK Cabinet did give Ms May a green light for action to deter the use of chemical weapons following a two-hour meeting on Thursday afternoon.

Every member of the prime minister’s top team was said to have spoken during the meeting, which gave unanimous backing to the “the need” to intervene.

But an early attack would intensify domestic pressure on the prime minister, who faces demands from her own back benches and from Mr Corbyn and other party leaders to allow Parliament a vote prior to any action.

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On Friday morning the Labour leader said: “Further UK military intervention in Syria's appalling multi-sided war risks escalating an already devastating conflict.

“The government appears to be waiting for instructions from President Donald Trump on how to proceed. But the US administration is giving alarmingly contradictory signals.”

Mr Corbyn repeated a call for the Commons to be given a vote, with MPs due to return to Westminster on Monday.

He went on: “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.

“Rather than further military action, what is urgently needed is a coordinated international drive to achieve a ceasefire and a negotiated settlement under UN auspices.”

Russia has been granted a request for the United Nations Security Council to meet on Friday for fresh discussions on the potential fallout from air strikes on Syria.

Mr Macron, due to speak to Mr Trump on Friday, also laid the ground for action, undertaking a round on interviews in which he said he had proof the Assad regime was responsible for an air strike involving chemical weapons on civilians in Douma.