Russia proposes 48-hour 'humanitarian pause' in Aleppo

Russia said it will agree to a 48-hour ceasefire in Syria's northern city of Aleppo, but has rejected a US proposal for a seven-day truce, a top official said on Thursday.

Russia's Deputy Foreign Affairs Minister Sergei Ryabkov said a seven-day pause in Aleppo will enable rebel factions to "regroup".

Ryabkov also dismissed US' threat to halt cooperation with Russia in Syria's war as an "emotional breakdown", accusing the US of supporting "terrorists."

"We cannot interpret this as anything else apart from the current US administration's de facto support for terrorism," Ryabkov said.

"These thinly disguised invitations to use terrorism as a weapon against Russia show the political depths the current US administration has stooped to in its approach to the Middle East and specifically to Syria."

His comments come in response to the US' threat to halt cooperation with Moscow over Syria, unless Russian and Syrian regime strikes on Aleppo end.

Meanwhile, Syrian activists have said airstrikes on Aleppo on Thursday destroyed the last remaining bakery serving a town north of the besieged city.

A number of air raids hit the town of Anadan and its bakery, putting it out of service, the Syrian Observatory for Human Rights said.

Kerry has made the one threat the Russians feared most - the suspension of US-Russia bilateral talks about Syria. - John McCain and Lindsey Graham

Adnan Medlej, an activist from Anadan, said the bakery was hit shortly after it distributed bread to the town's remaining 2,000 residents and others in nearby villages.

After coming under intense bombing and devastating its infrastructure, most of the town's residents have fled to other areas in rural Aleppo.

A video shot by Medlej shows the bakery destroyed and a crater outside, with water leaking and walls torched.

On Wednesday, government shelling near a bread distribution center in the besieged Aleppo city killed six people.

Six people were killed in government shelling near a bread distribution center in Aleppo [AFP]

The UN envoy for Syria said the continued airstrikes leave little prospect of an imminent restart of negotiations to try to end the raging conflict.

"At the moment, when bombs are falling all over, it is very difficult to justify resuming talks," Staffan de Mistura told AFP.

The Swedish official said he had not given up all hope of re-establishing a ceasefire.

"I do recognise that sometimes in war you can talk and have the war going on," he said. "At this moment it is the breakdown of an agreement which was the beginning of a new phase.

Washington threatened to suspend its engagement with Russia following escalating bombardments on rebel-held parts of the city of Aleppo.

US Secretary of State John Kerry phoned his Russian counterpart on Wednesday to deliver the ultimatum after two hospitals were bombed in the morning by suspected Russian war planes.

Kerry's move was subject to mockery from Republican senators John McCain and Lindsey Graham.

"Finally, a real power move in American diplomacy. Secretary of State John 'Not Delusional' Kerry has made the one threat the Russians feared most - the suspension of US-Russia bilateral talks about Syria," the two commented sarcastically.

"We can only imagine that having heard the news, Vladimir Putin has called off his bear hunt and is rushing back to the Kremlin to call off Russian airstrikes on hospitals, schools, and humanitarian aid convoys around Aleppo."