The United States says it is working on specific initiatives to reduce the bloodshed in Syria and revive a nationwide ceasefire.
It says a priority is to halt conflict in Aleppo, where more than 200 people have died in a week of government air strikes and rebel shelling.
The US wants Russia to put pressure on the Syrian government to stop what it says is an indiscriminate bombardment.
Russia says the air raids on Aleppo are targeting terrorist groups.
US Secretary of State John Kerry dismissed Russian and Syrian government claims that the Aleppo strikes were targeting the Nusra Front - a jihadist force that is not party to a ceasefire.
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