President Donald Trump ordered military action against the Assad regime in Syria in response to the horrific Khan Sheikhoun chemical attack believed to have been carried out by government forces.

The Pentagon said 59 Tomahawk missiles were fired at an air base in Homs where aircraft that carried out the attack, possibly with sarin gas, are thought to have been housed. According to Reuters, Syrian state TV reported: "American aggression targets Syrian military targets with a number of missiles".

The missile strike was not announced earlier, but strong rhetoric had come out of the administration before the action was taken.

Secretary of State Rex Tillerson earlier told reporters that there was "no role" for Bashar al-Assad in governing Syria.

Tillerson said the chemical attack "violates all previous UN resolutions, violates international norms and long-held agreements between parties, including the Syrian regime, the Russian government, and all other members of the UN Security Council.

Following the action, Tillerson said: "We feel the strike itself was proportionate."

Speaking at the Mar-a-Lago resort in Florida, where he is currently holding a two day summit with Chinese premier Xi Jinping, Trump said that the strike was in the "vital national security interest" of the US.

"Years of previous attempts at changing Assad's behaviour have all failed and failed very dramatically," the president said.

"As a result the refugee crisis continues to deepen and the region continues to destabilise, threatening the US and its allies."

He added: "Tonight I call on all civilised nations in seeking to end the slaughter and bloodshed in Syria."

The UK government said the strike was "an appropriate response to the barbaric chemical weapons attack".

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US President Donald Trump delivers a statement about missile strikes on a Syrian airbase at his Mar-a-Lago estate in West Palm BeachCarlos Barria/Reuters

Moscow was informed ahead of the cruise missile strike on Shayrat airfield, Reuters reported.

Pentagon spokesman Captain Jeff Davis said: "Russian forces were notified in advance of the strike using the established deconfliction line. US military planners took precautions to minimise risk to Russian or Syrian personnel located at the airfield.

"We are assessing the results of the strike. Initial indications are that this strike has severely damaged or destroyed Syrian aircraft and support infrastructure and equipment at Shayrat airfield, reducing the Syrian government's ability to deliver chemical weapons.

"The use of chemical weapons against innocent people will not be tolerated," he added.

Homs Governor Talal Barazi told Reuters he does not believe the strikes caused "big human casualties", but said there is material damage. He went on to claim the attack amounted to "support for the armed terrorist groups, and it is an attempt to weaken the capabilities of the Syrian Arab Army to combat terrorism".

Defence officials said the strikes were launched from the USS Ross and USS Porter in the eastern Mediterranean Sea.

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Navy guided-missile destroyers USS Ross (top) and USS PorterMurad Sezer/Reuters
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US Navy guided-missile destroyer USS Ross (DDG 71) fires a tomahawk land attack missile on 7 April 2017Robert S Price/Courtesy US Navy/Handout via Reuters

Senators John McCain and Lindsey Graham released a joint statement praising the move, saying that the US military "have sent an important message the United States will no longer stand idly by as Assad, aided and abetted by Putin's Russia, slaughters innocent Syrians with chemical weapons and barrel bombs."

"Unlike the previous administration, President Trump confronted a pivotal moment in Syria and took action. For that, he deserves the support of the American people."