David Cameron has said he and Russian president Vladimir Putin share "fundamental aims" in seeking an end to the bloodshed in Syria.
Speaking during a joint press conference in the Black Sea resort of Sochi, the prime minister said the situation in Syria was "appalling and deteriorating".
He said: "It's no secret that we have had differing views on how best to handle the situation but we share fundamental aims: to end the conflict, to stop Syria fragmenting, to let the Syrian people choose who governs them and to prevent the growth of violent extremism."
Mr Cameron also announced that the UK and Russia had agreed there should be "limited co-operation" between their security services in the build-up to the Winter Olympics in Sochi next year.
Mr Cameron said: "The history of Syria is being written in the blood of her people."
The prime minister welcomed the US-Russian agreement to hold a special conference aimed at delivering a "transitional government based on the consent of the Syrian people as a whole".
He added: "The president and I have agreed that, as permanent members of the United Nations, we must help to drive this process, working with partners in the region and beyond, not just bringing the regime and opposition together at one negotiating table but Britain, Russia, America and other countries helping shape a transitional government that all Syrians can trust to protect them.
"We urgently have to do more for the sake of the people of Syria to break the vicious cycle that threatens to destroy Syria and that threatens to export violence and extremism around the world."
Mr Cameron set out plans for security co-operation ahead of the Sochi Games as he met Mr Putin at the President's summer residence in the city.
He said: "We both want the Sochi Games to be a safe and secure Games. So today I have agreed with President Putin that there should be limited co-operation between our security services for the Sochi Olympics."
The prime minister said his talks with president Putin had been "very substantive, very purposeful, very useful".
But he acknowledged: "Of course, it is no secret that there are issues where we differ. We don't duck these, we have had very frank discussions, as we have today.
"But a more effective relationship will help make people in both our countries safer and better off and that is what we have been focusing on today."
Mr Cameron's agreement to British security involvement ahead of the Sochi games marks the first co-operation between UK and Russian spies since links were broken over the 2006 murder of Alexander Litvinenko.
The UK offered assistance to the Russian Federal Security Service (FSB) following a fatal bombing in the Moscow airport of Domodedovo in 2011, but the Russians rejected the offer, a Foreign Office spokesman said.
Mr Putin thanked Mr Cameron for their "substantive and frank" talks, but was more cautious in his wording when it came to discussing the situation in Syria.
The Russian president said: "We have common interest in putting an immediate end to violence in that country and launching the peace settlement in preserving Syria as an integral and sovereign state.
"We discussed a number of steps and options to resolve the crisis."
In the joint statement after the talks, he focused instead on increased trade and investment between the UK and Russia, and a cultural exchange programme which will take place in London and Moscow in 2014.
He also thanked the UK for its help in preparing for the Sochi 2014 Winter Olympic Games following the staging of the event in London last summer.
He said: "More than 60 British companies are involved in the preparation for the Sochi 2014 games. They are quite successful and we are grateful to our British partners."