David Cameron has claimed that Vladimir Putin explicitly called for Syria's President Bashar al Assad to go - but his comments have been denied by Moscow.
Speaking after a meeting with Mr Putin at the G20 summit, the Prime Minister said that Russia's president no longer backs Mr Assad .
He said: "There are main differences over sequencing the exact shape of how the transition takes place but it is welcome that President Putin has been explicit he is not locked in to Assad remaining in charge in Syria.
"What we need next is an agreement on a transitional leadership which can move Syria towards a democratic future which protects the rights of all its communities."
But his comments have prompted disagreement from Moscow, with foreign minister Sergei Lavrov saying they "don't correspond to reality".
Mr Putin also appeared to contradict Mr Cameron at the meeting of the leaders of 20 major economies in Mexico.
He said: "No one has the right to decide for other people who should be in power and who should step aside.
"It is not changing the regime that is important, but that after changing the regime, which should be done constitutionally, violence is stopped and peace comes to the country."
Sky's Mark Stone said the confusion is "potentially very embarrassing for David Cameron" and could be a result of the difference in language.
"There is clear differences depending of which translator did the translation of President Putin," he said.
Syria has been one of the top issues on the agenda at the G20, as shelling and clashes between rebel fighters and government troops in the country continues.
Mr Cameron also said that "it makes no sense" to supply weapons to Syria, as news emerged that a Russian-operated ship thought to be carrying attack helicopters bound for Syria was forced to turn back after its British insurer withdrew its cover.
The move was welcomed by Mr Cameron, who joined with the US and other countries in pressing Russia to stop shipping arms to the Assad regime.
"It makes no sense for any country to be supplying arms to a regime that is killing its own people with mortars, snipers and attack helicopters," he said.
"It is good news that the shipment of attack helicopters we've been tracking in the North Sea in recent days is heading away from Syria.
"But we will continue to work to stem the flow of weapons."
UK-based insurer Standard Club said that after it became aware that the ship was carrying munitions - a breach of its rules - it removed its insurance coverage.
The vessel, named MV Alaed, has "turned back now apparently toward Russia", according to Foreign Secretary William Hague.
Moscow has not commented on the ship or its reported contents.
The UN's observer mission in Syria, meanwhile, said that despite coming under fire numerous times recently, his forces are "morally obliged" to remain in the country.
After a private briefing of the Security Council, Major General Robert Mood said that questions about cancelling the mission were premature.
"We are not going anywhere," he said.
"Shelling, small arms fire and other incidents are coming much closer, and we have been targets several times over the last few weeks.
"The suffering of the Syrian people, the suffering of men, women and children, some of them trapped by fighting, is getting worse."
On Saturday, the UN said it was suspending all missions in the country because of concerns for the safety of its 300 observers, after the levels of violence increased.
Major General Mood said that a reduction in violence would be needed before the missions were restarted, as well as commitment from the Syrian government and opposition that observers would have "freedom of movement".
