Boris Johnson has called for targeted sanctions against Syria and Russian diplomats until Assad is ousted, but the G7 has said President Putin "must not be backed into a corner" as it continues to seek diplomatic solutions.
US Secretary of State Rex Tillerson told Mr Putin that he hoped for a joint G7 position against Assad and expected support from Middle Eastern allies in the wake of the deplorable chemical gas attack that killed 87 people a week ago.
Mr Tillerson, on a visit to Moscow, will say Russia's alliance with Iran and Syria does not serve President Putin's own interests – it comes after two Russian servicemen were killed in a mortar strike in Syria within the last few minutes.
Another soldier remains in hospital.
But sanctions against Russia, which has been propping up Bashar al-Assad's regime for some time now, and Syria, will not be implemented until a thorough investiagtion into the chemical weapons attack on the rebel held area of Khan Sheikhun has taken place.
Italian foreign minister Angelino Alfano said the G7 had spoken with representatives from Saudi Arabia, Jordan, Qatar and Turkey, something he hailed as "a political success".
He said: "We had a very productive and fruitful meeting, especially as it took place right before the departure of Rex Tillerson to Moscow.
"We must have a dialogue with Russia and not push Russia into a corner and must ask Putin to put Russian strength on Assad and get him to observe the commitments with regard to the ceasefire."
Boris Johnson called for sanctions after the Syria attack, but G7 members disagreed
Boris Johnson has pushed for sanctions against Syria after chemical weapons attack
Mr Johnson is taking a harder stance on the Assad regime than the rest of the G7 nations.
He said: "The regime of the Assad family is coming to an end. What happened last week was a chemical weapons attack by Assad on his own people.
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"It seems approproate for ecominic and individual sanctions on the basis of that."
In a warning to the Kremlin, Mr Johnson said: "Russia is sticking with this guy [Assad] and it's damaging their reputaiton. Does Russia want to be part of the solution?
"I would like to see Russia engage in the process. Putin may have been betrayed by this guy he's been backing. We have no evidence Russia knew about or was involved in the chemical weapons attack."
He urged Moscow 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”.
Italian foreign minister Angelino Alfano wants to take a very diplomatic approach
A Downing Street spokesperson said: “The prime minister and the president agreed that a window of opportunity now exists in which to persuade Russia that its alliance with Assad is no longer in its strategic interest.
“They agreed that US secretary of state Tillerson’s visit to Moscow this week provides an opportunity to make progress towards a solution which will deliver a lasting political settlement.”
Germany’s foreign minister, Sigmar Gabriel, wants Russia and Iran involved in any ongoing peace process.
he said: "Not everyone may like it, but without Moscow and without Tehran there will be no solution for Syria."