The US says it is working on plans to reduce the bloodshed in Syria and revive a nationwide ceasefire.
It says its "top priority" is to halt conflict in the city of Aleppo, where at least 200 people have died in a week of government raids and rebel shelling.
The US wants Russia to put pressure on the Syrian government to stop what it says is indiscriminate bombardment.
Russia says the strikes in Aleppo are targeting terrorists, but confirmed it was discussing a truce there.
Negotiations are under way to include Aleppo in a temporary "regime of calm", Lieut Gen Sergei Kuralenko, who heads Russia's ceasefire monitoring centre in Syria, told Russian media.
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