US Secretary of State John Kerry has warned his Russian counterpart that Washington will end Syria talks unless Moscow stops the bombing of Aleppo.

In a phone call with Sergei Lavrov, Mr Kerry said the US held Russia responsible for the use of incendiary and bunker bombs against the city.

The US state department said it was making preparations to suspend talks.

Aleppo has come under heavy aerial bombardment since the end of a ceasefire a week ago.

In response to Mr Kerry's phone call, the Russian Deputy Ambassador to the UN, Evgeny Zagaynov, said the "trend" of Russia being blamed for the attacks in Syria must stop.

"It's become a sort of unfortunate tradition that the majority of strikes on civilian facilities in Syria, without checking it ... is blamed on Damascus or Russia,'' he said.

But Moscow said on Wednesday they would send diplomats to Geneva to talk to the US about normalising the situation in Aleppo.

"On orders of the Russian president, we are ready to continue joint work with our American partners on the Syrian issue," the defence ministry said in a statement.

Some 250,000 people are trapped in the rebel-held east of the city. They are under siege from Russian-backed Syrian government forces, which have launched a fierce campaign to recapture the area. The bombardment has been among the worst in the history of the five-year conflict.

The US has accused Russia of taking part in strikes on civilian targets and possibly committing war crimes.

The two nations have been locked in talks in an attempt to revive a fragile peace agreement, but the US said last week that Russia had openly lied to the UN about its intentions.