Russia said Thursday it was prepared to secure safe passage for rebels to quit Syria's Aleppo but kept up air strikes on the battleground city as world powers readied new truce talks.

Syria has been plunged into some of the worst violence of its five-year war since the collapse last month of a truce brokered by Washington and Moscow.

The ensuing surge in fighting has accompanied a large-scale government offensive, backed by Russian air power, to capture the opposition-held half of battered Aleppo.

Russia said Thursday it was willing to give rebels safe passage out of Aleppo, where over 250,000 people are under government siege.

"We are ready to ensure the safe withdrawal of armed rebels, the unimpeded passage of civilians to and from eastern Aleppo, as well as the delivery of humanitarian aid there," Russian Lieutenant General Sergei Rudskoy said in a televised briefing.

On the ground in the ravaged city, at least seven civilians were killed in a series of early morning strikes, the Syrian Observatory for Human Rights monitoring group said.

On the northeastern outskirts of the city, advancing regime troops captured several hilltops overlooking opposition-held areas.

An AFP correspondent in the besieged east said the strikes had resumed on Thursday afternoon.

Syrian state television said four children were killed by rebel rocket fire on a school in a western regime-held neighbourhood.

Residents in the west said they had been forced to pull over in their cars to take shelter in buildings because of the barrage of rebel fire.

Moscow has come under mounting international pressure over the rising civilian death toll from President Bashar al-Assad's Russian-backed campaign to take east Aleppo, including Western accusations of possible war crimes.

Since the army's assault began in late September, Russian and government bombardment has killed more than 370 people, including 68 children, according to an Observatory toll.

Shelling by rebel and Islamist militant groups, meanwhile, has killed 68 people in government-held areas.

Several major international efforts have failed to secure a political solution to Syria's brutal war, which has cost more than 300,000 lives.

A new diplomatic push will take place this weekend.

US Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov are expected to be joined at talks in the Swiss city of Lausanne on Saturday by their counterparts from Turkey, Saudi Arabia and Qatar -- all backers of Syrian opposition forces.

Then in London on Sunday, Kerry will likely meet up with his European counterparts from Britain, France and Germany.

UN Syria envoy Staffan de Mistura will also attend the Lausanne talks.

Lavrov told CNN television in an interview Wednesday that he hoped the discussions in Switzerland could help "launch a serious dialogue" based on the now-defunct US-Russian pact.

He also spoke Thursday with his French counterpart Jean-Marc Ayrault, despite tensions between the countries over Syria that prompted President Vladimir Putin to cancel a trip to Paris.

The French foreign ministry said Ayrault had stressed "the urgency to break the current impasse... and achieve a halt in the bombing in Aleppo".

Washington and Moscow had worked closely in recent months and reached a deal in mid-September that was billed as the "best chance" to end Syria's bloodshed.

That agreement envisioned a halt to hostilities, increased humanitarian aid to hundreds of thousands of besieged civilians across Syria, and unprecedented coordination between Moscow and Washington against Islamist militants.

But the truce fell apart after a week, and peace efforts have since struggled to get off the ground.

A French-drafted resolution was shot down by Russia in a stormy UN session last weekend.

Russian President Vladimir Putin hit out at Paris for the vetoed proposal, accusing it of deliberately putting forward a motion "fanning hysteria around Russia".

Putin dismissed accusations of possible war crimes as "political rhetoric" and warned Western countries against imposing sanctions on Russia.

Despite differences over Syria, Russia and Turkey have been pursuing closer ties and Assad welcomed the rapprochement in an interview with Russia's Komsomolskaya Pravda tabloid.

"I look positively to this relationship," he said in an excerpt of the interview.

"The only hope that we have as Syria is that Russia can make some changes in the Turkish policy."

Ankara has staunchly backed Syria's opposition and regularly demanded Assad step down.

It launched its own operation in Syria in August, targeting both the IS group and Kurdish fighters.