He was due to fly to Moscow tomorrow, the first visit by a UK foreign secretary in more than five years, for talks with counterpart Sergey Lavrov.
Instead he attacked the Kremlin and said he would focus on building support with allies to secure a ceasefire in war-torn Syria.
The missile strikes blasted an airfield believed to have been the launchpad for last week’s chemical weapons attacks on civilians, including children, for which the West blames Syria’s President Bashar al-Assad.
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We deplore Russia’s continued defence of the Assad regime
Yesterday US President Donald Trump tweeted: “Congratulations to our great military men and women for representing the United States, and the world, so well in the Syria attack.”
Mr Johnson said: “We deplore Russia’s continued defence of the Assad regime even after the chemical weapons attack on innocent civilians.
“We call on Russia to do everything possible to bring about a political settlement in Syria and work with the rest of the international community to ensure that the shocking events of the last week are never repeated.”
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Boris Johnson has cancelled his visit to Russia to meet Sergey Lavrov after US airstrikes
Mr Johnson had originally planned to travel to Moscow at the end of March, but rescheduled to attend a meeting with Nato counterparts, including US Secretary of State Rex Tillerson.
Russia has condemned the US strikes on the airbase in Shayrat as an act of “aggression against a sovereign state in violation of international law”.
Mr Tillerson will still go ahead with a visit to Moscow next week to deliver a “clear and co-ordinated” message to the Russians, Mr Johnson said.
He added: “Developments in Syria have changed the situation fundamentally.
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The US has launched airstrikes at a Syrian airfield base
My priority is now to continue contact with the US and others in the run-up to the G7 meeting on April 10 and 11 to build co-ordinated international support for a ceasefire and an intensified political process.”
An insider said Mr Johnson agreed that Mr Tillerson should go to Russia because it was the Americans who launched the airstrike, not the British.
It was also thought more prudent for Mr Tillerson to travel to Moscow because he will get face time with Russia’s President Vladimir Putin whereas Mr Johnson was only due to meet Mr Lavrov.
In return the former London mayor agreed to take the diplomatic lead with the G7 nations – Britain, the US, Canada, France, Germany, Italy and Japan – at tomorrow’s two-day meeting in Italy because he knows the world leaders better than Mr Tillerson, who was sworn in fewer than two months ago.
Mr Johnson said he would focus on building support with allies to secure a ceasefire in Syria
The source said: “Tillerson wants to be able to go to Moscow with the backing of the G7 and that’s where Boris comes in. He will lead the talks and galvanise support.
“The collective message from the G7 to Russia needs to be threefold: transition Assad away, get out of Syria and let’s help rebuild the country.
“We are in the strongest position we’ve ever been in after the US missile strike. We need to capitalise on that.
“When 59 Tomahawks hit Syria, it sends a very clear message not only to Assad but also to Russia. It makes Moscow realise Syria is no longer an asset and is more of a liability.”
There were already growing concerns that British talks with Russia would look bad in light of last week’s sarin attack on the rebel-held town of Khan Sheikhun in the Idlib province, which killed at least 74 people including 20 children.
Trump launches military strike against Syria Fri, April 7, 2017
U.S. President Donald Trump launched 59 Tomahawk missiles against Syria in response to its chemical attack on its own civilians
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Trump ordered a massive military strike against a Syria
Another Foreign Office source described last week’s events as a “game changer” and said the consensus was that Assad’s days were “numbered”.
The insider said: “The impunity Assad has had in murdering his own people – those days are over.
“If you commit war crimes, there are consequences. In 2013 Assad insisted that all chemical weapons had been removed from Syria. This once again proves that Assad cannot be part of the future. Sarin as a weapon of war, gassing babies to death?
“That crosses a line and after the US missile strike, there’s no going back.
“The only reason Assad is still there is because he is propped up by Russia. That has got to change.”
Syria’s President Bashar al-Assad has been blamed for the sarin gas attack
Yesterday Mr Tillerson said there was a plan to force Assad from office. However, the Trump administration has not yet spelled out how long the process will take to unseat one of the most tenacious leaders in the Middle East.
Turkey, which is already hosting three million displaced Syrians, welcomed the US military intervention and has urged Mr Trump to do more to get rid of Assad.
Saudi Arabian ruler King Salman bin Abdulaziz Al Saud called Mr Trump on Friday to express his support for the US attack, which he called a “courageous decision”.
Iranian President Hassan Rouhani called for an international fact-finding mission
Iranian President Hassan Rouhani yesterday called for an international fact-finding mission, signalling the regime may be having doubts about continuing to support Assad.
Iran and Russia have been the Assad government’s primary national backers during the six-year-old Syrian civil war.
● Prince Charles and his sons William and Harry will be among world leaders gathering in France today to mark the centenary of the four-day battle of Vimy Ridge, a defining battle during the First World War.