The UK is pushing G7 countries to collectively impose new sanctions on Russia if it does not cut ties with Bashar al-Assad amid the ongoing conflict in Syria.

Russian leader Vladimir Putin said he would “respond with force” if there were more US air strikes in Syria after President Donald Trump ordered the launch of 59 missiles against a strategic air base. The missiles came after Mr Assad sanctioned a chemical weapon attack, which killed more than 90 people, including women and children.

UK Foreign Secretary Boris Johnson wants “very punitive sanctions” for the chemical attack. A paper on sanctions has been prepared for a G7 meeting which begins in Italy on Monday.

He wrote on Twitter that he had cancelled a trip to Moscow, the priority being “talks with my G7 counterparts about Syria and Russia’s support for Assad”.

He also said President Trump had delivered a clear message from the West and “Crucially, they could do so again”, he told The Sun.

“We cannot miss this moment," he added.

“It is time for Putin to face the truth about the tyrant he is still propping up."

Sir Michael Fallon, the defence secretary, said he believed Russia was responsible for the chemical attack “by proxy”. If Russia refuses to cast off its relationship with Syria, G7 countries would impose more sanctions.

The Russian embassy in London said that if Moscow was given an ultimatum to take its forces out of Syria and cut ties with its leader this week it could result in “real war”.

But not everyone is as convinced as Mr Johnson that the US was attempting to send a “clear, united message”.

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Seth Abramson, a professor at the University of New Hampshire, said there was “overwhelming” evidence that Mr Trump’s military strike was “just an empty political gesture”, adding that the US communicated the strike with Russia beforehand.

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 result of giving both Russia and Syria advance notice of the air strike was that they moved their troops and bunkered their planes,” he wrote on social media.

Mr Trump left one runway on the air base untouched, even though he said he targeted the air base as he believed it was responsible for the chemical attack. He has not announced that he will send more humanitarian aid or increase the number of Syrian refugees, who he tried and failed to ban indefinitely from entering the US after stepping into the White House.

Boris Johnson: Syrian chemical attack evidence points to Assad

Joining Mr Johnson in Lucca, Italy, will be US Secretary of State Rex Tillerson, and both are working to put private and public pressure on Russia to withdraw support for Mr Assad, as well as their counterparts from Canada, France, Germany, Japan, Italy and the EU.

Italian Foreign Minister Angelino Alfano, who is hosting the meeting, said Europe broadly supported the US air strikes, which would set the meeting off to a more positive start.

“We need to remember that not 10 years ago, but 100 or 120 days ago, the concern in Europe was that the United States and the EU were moving apart,” Mr Alfano told Sky TG24. “I welcome this renewed harmony.”

Mr Tillerson, who said Washington will hold to account “any and all who commit crimes against the innocents anywhere in the world”, will then convey the message to Mr Putin on Wednesday.

US Secretary of State Rex Tillerson arrives to attend a ceremony at the Sant'Anna di Stazzema memorial (Reuters)

He is seen by some as a stronger opponent of Russia than his boss, as he also told CBS that Russians “have played now for some time the role of providing cover for Bashar al-Assad's behaviour”.

The US is considering executing extra sanctions on Russia, but conflicting messages came out of Washington DC during the round of Sunday morning talk shows.

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While Mr Tillerson said the US stance on Syria had not changed, declaring the defeat of Isis as the first priority, US ambassador to the United Nations Nikki Haley told the same network that there would be no peace until Assad had left.

It is speculated that further sanctions on Russia would not have much punch while the nation still dominates gas pipelines in eastern European gas.

Mr Johnson’s allies are confident in the UK Government’s ability to reign in Russia, despite Prime Minister Theresa May not releasing a comment on whether she supports new sanctions, and ar confident in Mr Trump's strategy.

Conservative MP Andrew Mitchell told Sky News that Mr Trump was “decisive, I think he was proportionate and absolutely right to do what he did”. He added that “all of us around the world can sleep more safely knowing that international law is being asserted”.