US Secretary of State John Kerry says a fragile partial truce in Syria has reduced levels of violence there, but that he wants to see a further reduction as well as greater flows of humanitarian aid.
Kerry was speaking at the start of a meeting in Moscow on Thursday with Russian Foreign Minister Sergei Lavrov, and will later meet Russian President Vladimir Putin.
Peace talks in Geneva between representatives of the Syrian government and opposition are bogged down, and Washington believes that Moscow, closely allied to Syrian President Bashar al-Assad, can nudge Damascus to make concessions.
"It's fair to say three weeks ago there were very, very few people who believed a cessation of hostilities was possible in Syria," Kerry told Lavrov at the start of their talks in Moscow.
"The result of that work has produced some progress. There has been a fragile (yet) nevertheless beneficial reduction in violence."
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Kerry said there was a hope that his meetings in Moscow could "further find and chart the road ahead so that we can bring this conflict in Syria to a close as fast as possible."
Russia and the United States have emerged as the two outside powers with a decisive say in what happens next in Syria's five year-old civil conflict.
The United States and its allies has been backing armed groups that rose up against Assad's rule, while Moscow has asserted its role with a five-month military campaign that turned the tide of the fighting in Assad's favour.
Kerry said he was looking forward to constructive conversations with Lavrov and Putin, and said it was encouraging that Russia and the United States were able to co-operate "despite differences ... in the face of this urgency to do what is necessary to meet the challenge."
Commenting on the cessation of hostilities, Lavrov said: "Our cooperation on Syria, our persistence allowed us to succeed because we worked by forming a balance of interests, not only those of Moscow and Washington but also of all the sides involved both in Syria and outside it."
