President Donald Trump has cleared his scheduled trip to the Summit of the Americas to concentrate on a response to Syria after an apparent chemical weapons attack on civilians by government forces.

Vice President Mike Pence is to take his place in Peru for the 8th Summit of the Americas and a trip to Colombia while Trump remains in the US to monitor developments, his press secretary said.

In a statement, Sarah Huckabee Sanders said: "The President will remain in the United States to oversee the American response to Syria and to monitor developments around the world."

On Monday, he vowed to respond "forcefully" to Saturday's apparent poisonous gas attack on civilians in Duma.

Mr. Trump told reporters during a Cabinet meeting that the administration would be making a "major" decision on Syria within the next 24 to 48 hours.

He added: "We are going to make a decision tonight or very shortly thereafter. And you'll be hearing the decision.

"We can't let atrocities like we all witnessed... we can't let that happen in our world.

"We can't let that happen, especially when we are able to - because of the power of the US, because of the power of our country - we are able to stop it."

Prime Minister Theresa May spoke to French President Emmanuel Macron about a response to Syria on Tuesday and said she was due to also speak to Mr Trump.

She has described the attack as "barbaric", adding: "If it is the responsibility of Assad's regime then it's yet another example of the brutality and brazen disregard for their people they show."

Mrs May said: "I spoke this morning to President Macron, I will be speaking later today with President Trump and the National Security Council meets regularly, and I'll be chairing a meeting of the National Security Council later today, and we'll be working with our allies as I say, crucially, to make an assessment of what has happened on the ground."

Labour leader, Jeremy Corbyn said: "I think the intervention ought to be to support the United Nations in undertaking an investigation into the chemical weapons attack. That's what the UN has called for.

"But, also, there has to be a political solution in Syria. That does mean the US and Russia, instead of engaging in megaphone diplomacy across the floor of the Security Council, saying they will support the reconvening of the Geneva talks and all the countries in the region getting round the table together."