In a development demonstrating the perils of journeying in the war-wracked country, at least 17 people -- most of them rebels -- died in a car bomb blast at an opposition checkpoint in northern Aleppo province on Thursday, a monitor said.
The blast hit near the town of Azaz close to the border with Turkey, the Britain-based Syrian Observatory for Human Rights said, adding that 14 of the dead were rebel fighters. It said the toll could rise.
The Islamic State group has regularly targeted rebel factions with bomb attacks, including an October 6 attack at a border crossing in neighbouring Idlib province that killed 29 rebels.
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.
Early morning raids in east Aleppo killed at least seven civilians, the Observatory said, and regime forces captured high ground overlooking opposition areas on the northeastern outskirts of the city.
The Observatory also said five children were killed by rebel rocket fire on western regime-held neighbourhoods, with state television saying a school had been hit.
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.
- Fresh truce talks -
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.
Analysts said Thursday's offer was simply a gambit to relieve the pressure by appearing to present diplomatic alternatives.
"There is no change in the Russian strategy: the goal remains the destruction of rebel presence in Aleppo," said Syria expert Thomas Pierret.
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"Blowing hot and cold allows them to reduce the pressure and empower those who want a strictly diplomatic approach to the Syrian question," he told AFP.
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 jihadist 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.
As key powers geared up for a new round of talks, newly-appointed UN chief Antonio Guterres said Thursday it was time to overcome divisions over ending the war.
"Whatever divisions might exist, now it's more important to unite," Guterres said. "It is the moral obligation of us all to stop the suffering of the Syrian people."
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.
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.
- 'Fanning hysteria' -
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.
But the truce fell apart after a week, and peace efforts have since struggled to get off the ground.
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.
"The only hope that we have as Syria is that Russia can make some changes in the Turkish policy," he said.
Saudi Foreign Minister Adel al-Jubeir, whose country like Turkey supports the opposition and has long called for Assad's ouster, also welcomed the Ankara-Moscow rapprochement.
"We see the reduction in tension between Turkey and Russia as perhaps an opportunity" that could help a solution in Syria, said Jubeir.