Trump's secretary of state to pressure Russia to end support for Assad
Fears US position weakened after G7 decision to postpone any sanctions
Western efforts to put pressure on Vladimir Putin over his support for Syria's President Bashar Assad will continue on Wednesday, despite divisions over the imposition of fresh sanctions.
US Secretary of State Rex Tillerson is in Moscow for talks after a G7 foreign ministers' meeting in Lucca, Italy.
It called on Russia to promote a "real and genuine" political process in Syria and to use its influence to end the country's bloody six-year civil war.
However Russian leader President Putin showed little inclination to respond to the US initiative, saying he was aware of planned "provocations" to blame Syria's government for using chemical weapons.
"It reminds me of the events in 2003 when US envoys to the Security Council were demonstrating what they said were chemical weapons found in Iraq," he told reporters.
"We have seen it all already."
Foreign Secretary Boris Johnson has come under fire over his handling of the G7 gathering, which put off decisions on any further sanctions until the outcome of an investigation into the chemical weapon attack.
Italian foreign minister Angelino Alfano told the closing news conference: "We must have a dialogue with Russia and we must not push Russia into a corner.
"There is no consensus on additional new sanctions as an efficient instrument to deliver the goal we are aiming for."
Mr Johnson had gone into the meeting saying ministers would discuss targeted sanctions against senior Russian and Syrian military figures implicated in last week's chemical weapons attack on the rebel-held town of Khan Sheikhoun.
He insisted the option of sanctions remained on the table and said there would now be an investigation by the Organisation for the Prohibition of Chemical Weapons.
"After that, if of course we can find people, whether they are Syrians or whether they are Russians associated with the Syrian military operation, it is in my view wholly appropriate that they should face economic sanctions or sanctions of some other kind," he said.
"That is something that had wide acceptance around the table last night, but you have got to do things in the proper legal way."
But former foreign secretary Sir Malcolm Rifkind told BBC Two's Newsnight he had misgivings about the US-UK push for sanctions.
"I always was a bit suspicious about its wisdom because there has to be some doubt about whether further sanctions would make any impact given that they were going to be targeted against individuals and unlikely to change the Kremlin's view," the Tory said.
"But also what we have now got is a worse situation than we started off with because Tillerson will now be told by the Russians, when he sees (Russian foreign minister Sergey) Lavrov 'well, you don't even have the G7 supporting you'."
Former UK ambassador to Washington Sir Christopher Meyer told the programme: "All we can say is he got himself out on a limb and the branch was cut off in Lucca, Italy at the G7 meeting."
Before his meeting with Mr Lavrov, Mr Tillerson said the Assad regime would fall and Moscow needed to decide which side it was on.
"It is clear to all of us that the reign of the Assad family is coming to an end.
"But the question of how that ends and the transition itself could be very important in our view to the durability, the stability inside of a unified Syria," he said.
"Russia has really aligned itself with the Assad regime, the Iranians and Hezbollah.
"Is that a long-term alliance that serves Russia's interest, or would Russia prefer to realign with other Western countries and Middle East countries who are seeking to resolve the Syrian crisis?
"We want to create a future for Syria that is stable and secure. Russia can be a part of that future."
The US officials raised the stakes before Mr Tillerson's visit to Moscow with the disclosure that the administration had reached the preliminary conclusion that Russia knew in advance of the chemical weapons attack on Khan Sheikhoun, which left at least 80 dead.
The White House, meanwhile, made clear that it could mount further strikes against the regime if there was any fresh use of chemical weapons, despite a threat of retaliation from Russia and Iran.