After months of sharp differences, Russia and the United States have agreed to push both sides in Syria to find an end to the bloodshed, offering to hold an international conference in search of peace.
Syrian rebels meanwhile said they had seized four Filipino peacekeepers in the Golan Heights, the second time in two months that UN troops have been abducted in the tense ceasefire zone between Syria and Israel.
In talks that stretched late into Tuesday night, US Secretary of State John Kerry met first for more than two hours with President Vladimir Putin and then for a further three with Foreign Minister Sergei Lavrov.
"We agreed that Russia and the United States will encourage both the Syria government and opposition groups to find a political solution," Lavrov told reporters at a concluding news conference that ended after midnight.
Lavrov and Kerry said they hoped they could convene an international conference by the end of May to build on the Geneva accord agreed by world powers last June for a peaceful solution in Syria.
The Geneva agreement, which was never implemented, set out a path toward a transitional government without ever spelling out the fate of President Bashar al-Assad.
The six-point accord -- negotiated by the last UN-Arab League envoy to Syria Kofi Annan -- "should be the road map... by which the people of Syria can find their way to the new Syria and in which the bloodshed, the killing, the massacres can end", Kerry said.
"The alternative is that there's even more violence, the alternative is that Syria heads even closer to the abyss, if not over the abyss and into chaos," Kerry warned, of a conflict that has already claimed over 70,000 lives.
And in what appeared to be a major concession to Russian concerns of instability in its Middle East ally, Kerry seemed to soften the US stand on Assad's future.
Washington has long insisted Assad must go.
But Kerry told reporters that only the Syrian regime and the opposition can determine the make-up of a transitional government to shepherd the war-torn nation towards democratic elections.
"It's impossible for me as an individual to understand how Syria could possibly be governed in the future by the man who has committed the things that we know have taken place," Kerry said as he wrapped up his first visit in office to Russia.
"But I'm not going to decide that tonight, and I'm not going to decide that in the end."
Lavrov said both Russia and the United States were ready to use all their resources to bring "the government and opposition to the negotiating table".
Russia has long accused the West of worsening the Syria conflict by seeking to topple the Assad regime.
The US and other Western states have in turn accused Russia of failing to use its influence with the regime to halt the bloodshed and keeping up military deliveries to Assad.
In one of the first reactions to the Russian-US accord, Lakhdar Brahimi, the UN-Arab League envoy for Syria, described the deal as a "very significant first step".
The United Nations said the four abducted peacekeepers were seized by an unidentified armed group while they were patrolling in the Golan Heights, and that efforts were under way to secure their release.
UN Secretary General Ban Ki-moon strongly condemned the attack, which came after Syrian rebels seized 21 Filipino peacekeepers for four days in March in the same ceasefire zone.
The Philippines said the represented a "gross violation" of international law and urged the UN Security Council to "use its influence for the early and safe release" of the four.
Israeli Defence Minister Moshe Yaalon said Tuesday his country was not getting involved in Syria's civil war, but insisted the Jewish state would not permit the transfer of arms to Damascus ally Hezbollah in neighbouring Lebanon.
Yaalon was speaking just days after two Israeli air strikes near Damascus sent regional tensions soaring and as the United Nations protested about Israel warplanes overflying Lebanon.
The raids struck several military targets in the early hours of Friday and Sunday and may have been carried out by Israeli warplanes from Lebanese air space.
Syria was cut off from the Internet on Tuesday, according to US tech firms monitoring Web traffic and the State Department.
The reasons were not immediately clear, but a similar blackout happened in November. According to activists, sudden communication cuts may occur before major military offensives.