US missile strikes on a Syrian airfield risk escalating the civil war in the region still further, the Labour leader Jeremy Corbyn has said.

Describing the nerve gas attack on the Idlib province of the war-ravaged region as a “horrific war crime”, Mr Corbyn added there was a need for an urgent independent United Nations investigations and that those responsible “must be held to account”.

But he added: “Unilateral military action without legal authorisation or independent verification risks intensifying a multi-sided conflict that has already killed hundreds of thousands of people.

“What is needed instead is to urgently reconvene the Geneva peace talks and unrelenting international pressure for a negotiated settlement of the conflict.

“The terrible suffering of the Syrian people must be brought to an end as soon as possible and every intervention must be judged on what contribution it makes to that outcome.

He also urged Theresa May to urge restraint on the Trump administration and “throw its weight behind peace negotiations and a comprehensive political settlement".

On Thursday Mr Corbyn had called for the various protagonists of the Syrian war to come together around the negotiating table in Geneva in order to bring peace to the war-ravaged region and end the six-year civil war, which has claimed the lives of more than 300,000 people.

"I think that's best brought about by looking at the sources of support for the various protagonists in the war, the role that's played by neighbouring states, by Russia and others, but basically, get around the table in Geneva."

His comments risked opening divisions in the party, however, after his deputy, Tom Watson, backed the United States’ military assault on the airbase near Homs in the early hours of Friday for appearing to be a “direct and proportionate response to a clear violation of international law” the Syrian regime.

U.S. airstrikes on Syria, explained

Mr Watson told the Birmingham Mail: "It's clear from the nerve gas attack in Khan Sheikhoun earlier this week that President Assad had retained a chemical weapons capability, contrary to what was agreed in 2013.

“Indiscriminate chemical weapons attacks on civilians can never be tolerated and must have consequences. It's vital that the United States is now clear about its intentions and that the whole international community works towards a political settlement in Syria.”

But Stop the War Coalition, which Mr Corbyn used to chair, called for an emergency protest outside Downing Street on Friday evening over the assault, which it described as “xenophobic and reactionary” and the “worst possible way” to respond to the nerve gas attack on the village of Khan Sheikhun.

In a statement, the group added: “As well as deeping the tragedy of the Syrian people, this utterly irresponsible act threatens to widen the war and lead the West into military confrontation with Russia.”

Michael Fallon, the Defence Secretary, earlier urged Russian officials to use its influence over Assad and “learn from what happened last night”. But he denied that the US offensive was the start of a new military campaign in Syria and was rather intended to deter the Syrian dictator from carrying out any further chemical weapons attacks.

He also confirmed the UK was in close contact with Mr Trump’s administration throughout Thursday and informed of the decision to strike the airfield in advance.

“This strike was very limited to one airfield,” Mr Fallon added. “It was entirely appropriate, it’s designed to deter the regime from carrying out further chemical weapons attacks. So we don’t see it as the start of a different military campaign.”

"President Assad and the Syrian regime have continued to flout international law. We've caught them using chemical weapons and gases elsewhere, and this latest incident in which nearly 100 people seem to have been killed is yet another example of, if action is not taken, innocent civilians are going to die at the hands of this appalling gas.

His comments were echoed by Downing Street, who insisted the UK Government “fully supports” the military assault, adding they believed “was an appropriate response to the barbaric chemical weapons attack launched by the Syrian regime, and is intended to deter further attacks”.

Tim Farron, the Liberal Democrat leader, said the assault on the Syrian airfield was a “proportionate response to the barbarous” attack by the Syrian government on its own people.

In pictures: US missile strike against Syria Show all 7 1 /7 In pictures: US missile strike against Syria In pictures: US missile strike against Syria The guided-missile destroyer USS Porter (DDG 78) launches a tomahawk land attack missile in the Mediterranean Sea AP In pictures: US missile strike against Syria The United States military launched at least 50 tomahawk cruise missiles at al-Shayrat military airfield near Homs, Syria, in response to the Syrian military's alleged use of chemical weapons in an airstrike in a rebel held area in Idlib province EPA In pictures: US missile strike against Syria Shayrat airfield in Syria Getty Images In pictures: US missile strike against Syria US Navy guided-missile destroyer USS Ross (DDG 71) fires a tomahawk land attack missile in Mediterranean Sea Reuters In pictures: US missile strike against Syria US Navy guided-missile destroyer USS Ross (DDG 71) fires a tomahawk land attack missile in Mediterranean Sea Reuters In pictures: US missile strike against Syria President Donald Trump speaks at Mar-a-Lago in Palm Beach, Fla., after the US fired a barrage of cruise missiles into Syria in retaliation for this week's gruesome chemical weapons attack against civilians AP In pictures: US missile strike against Syria Syria's President Bashar al-Assad Reuters

“The British Government rather than just putting out a bland statement welcoming this should now follow it up and call an emergency meeting of the Nato alliance to see what else can be done, be that more surgical strikes or no fly zones. Evil happens when good people do nothing, we cannot sit by while a dictator gasses his own people. We cannot stand by, we must act.”

Paul Nuttall, the Ukip leader. added he “hoped for better from this administration” and that the action was “rash, trigger happy, nonsensical and will achieve nothing”.