More than 250 civilians have been killed in Aleppo in Syria in the last 10 days.
The US wants Russia to put pressure on its ally the Syrian government to stop what it says is indiscriminate bombardment.
The Russian and Syrian governments say the Aleppo strikes are targeting the Nusra Front – a jihadist force not party to a ceasefire agreed in February.
As a top priority, John Kerry said, was ending the violence in the northern city of Aleppo.
Mr Kerry is due to hold urgent talks on the situation with the UN envoy to Syria, Staffan de Mistura, and the Saudi and Jordanian foreign ministers.
A Russian defence official said earlier that negotiations were taking place to establish a ceasefire there.
