BORIS JOHNSON tonight declared America was willing to strike Syria again – as the Russians warned of 'real' war against the West.

Speaking exclusively to the Sun, the Foreign Secretary said the US had “delivered a clear and united message” from the West in bombing Syria last week.

3 Boris Johnson warns the US could strike Syria again in a bid to oust Assad Credit: Getty Images

And on the eve of a critical G7 Summit expected to threaten Russia with new sanctions, he said: “Crucially – they could do so again”.

Mr Johnson praised US President Donald Trump for showing “a resolve and willingness that has been sadly missing in the last few years”.

He said: “We cannot miss this moment. It is time for Putin to face the truth about the tyrant he is still propping up.”

3 Boris praised Donald Trump over his decision to strike in Syria Credit: AP:Associated Press

Russia, Iran and other allies of the Assad regime accused the US of “crossing red lines” over airstrikes in response to a chemical attack on a rebel-held village.

In a joint statement they said: “We will respond with force to any aggressor.”

And the Russian Embassy in London raised the prospect of war in a series of provocative tweets that described Johnson as Trump's "lieutenant".

If G7 ultimatum to Russia brings us to real war,what is your trust in @realDonaldTrump as a wartime leader&@BorisJohnson as his lieutenant? — Russian Embassy, UK (@RussianEmbassy) April 9, 2017

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In one it suggested “conventional war” could be an outcome if G7 delivers an ultimatum this week.

Mr Johnson and other foreign secretaries meet in Italy on Monday to agree a plan US Secretary of State Rex Tillerson will take to Moscow on Wednesday.

Punitive sanctions will also be threatened - in a repeat of the tactic used in the Ukraine conflict. One aide said they could 'cripple' the Russian economy.

Mr Johnson was ridiculed by opponents on Saturday after pulling out of a visit to Russian capital planned for Monday. Former SNP chief Alex Salmond said it appeared Boris Johnson was in “deep political trouble”.

But aides insisted the Foreign Secretary had discussed tactics with US Secretary of State Rex Tillerson at length.

And Boris Johnson told the Sun that critics “carping and using the death of civilians in a gas attack to fire off personal insults” were only emboldening the Russians and Assad.

And he stormed: “I am focussed on working with the US and getting the G7 behind the goal of ending this war and rebuilding Syria – one Rex Tillerson will deliver for the whole of the G7 to Russia.”

He added: “There is no doubt that the US action is a game changer in Syria.

“We need to make it clear to Putin that the time to back Assad has gone.

“By continuing to support a man who gasses his own people he is damaging Russia further in the eyes of the world.

“He must now understand that Assad is now toxic in every sense.

“He is poisoning the innocent people of Syria with weapons that were banned 100 years ago. And he is poisoning the reputation of Russia.”

3 Boris warned by supporting Assad, Vladimir Putin is damaging Russia further in the eyes of the rest of the world Credit: AP:Associated Press

Vladimir Putin spoke to Iran’s Hassan Rouhani. The Kremlin said the pair agreed the US airstrikes breached international law.

The two leaders also called for an objective investigation into the chemical attack on the village of Khan Sheikhun in Syria’s rebel-held Idlib province.

But US Secretary of State Rex Tillerson joined Britain in blaming Russia for the horrific chemical attack that claimed the lives of 100 Syrians last week. He hinted the White House’s first priority was finishing off ISIS.

But one senator said Assad was saying ‘F*** y**’ to the US by continuing to fly jets from the airfield bombed by the US on Friday morning.

Defence Secretary Michael Fallon had earlier said Russia was to blame for “every civilian death” in last week’s brutal chemical attack.

Writing in the Sunday Times he said Russia was responsible “by proxy” as the “principle backer” of President Bashar al-Assad’s regime.