Russia's credibility 'at stake' over Aleppo offensive: White House

White House spokesman Josh Earnest blamed Russia for the Syrian regime's non-compliance with the short-lived ceasefire.

"Russia's culpable, and if this arrangement has a future, Russia's going to need to step up and prove it," Earnest told reporters in a daily briefing.

Meanwhile, the Syrian civil defence reported dozens of civilian deaths on Friday.

"Ninety civilians, including children, were killed and dozens more wounded in raids on eastern Aleppo by Russia warplanes and regime aircraft on Friday," said Ibrahim al- Hajj, the media centre director for the Syria civil defence told The New Arab.

The Syrian Observatory for Human Rights documented 45 deaths on Friday.

The intensity of the bombardment, which included artillery barrages and barrel bombings by helicopters, brought new misery to the estimated 250,000 civilians besieged by the regime's army.

The escalation came after US Secretary of State John Kerry failed to reach an agreement with Russian counterpart Sergei Lavrov on Thursday on terms to salvage a failed ceasefire.

The two met again on Friday at the United Nations and made what Kerry said was "a little bit of progress" on resolving their differences on Syria.

"We're evaluating some mutual ideas in a constructive way, period," Kerry told reporters.

Asked at the UN earlier whether the truce could be reinstated, Lavrov simply said: "You should ask the Americans."

Lavrov said there was "no alternative" to the Russian and US-led peace process and insisted that "now it is essential to prevent a disruption of these agreements."

The Syrian army declared an end to the truce on Monday following a US-led coalition strike on Syrian soldiers near Deir Ezzor that Washington said was unintentional.

The US-Russian ceasefire deal was further endangered by an attack on an aid convoy in Aleppo province on Monday the left 20 dead and destroyed 18 trucks.

The Syrian crisis will not be resolved unless the United States and its allies rein in opposition rebels fighting alongside the Islamic State group and the al-Qaeda-linked Nusra Front, Lavrov said.

"We will not be able to improve the humanitarian situation without the rooting out of the terrorist groups," he said.

From the UN podium, Lavrov asserted that Russia's military intervention helped "prevent the collapse of statehood and disintegration of Syria" that would have plunged the Middle East further in chaos.

Kerry told reporters that there had been "a little bit of progress" during talks on the effort to put the ceasefire back on track.

Agencies contributed to this report.