Russia Monday announced an eight-hour "humanitarian" ceasefire in Aleppo later this week, as the EU warned that the Syrian regime's Moscow-backed assault on the city could amount to war crimes.
The United Nations and European Union welcomed the announcement, but said Thursday's planned pause in fighting needed to be longer to allow the delivery of humanitarian aid.
In the latest violence, dozens of civilians including 12 members of the same family were killed in heavy bombardment of rebel-held eastern sectors of the embattled city, a monitoring group said.
"We have taken a decision not to waste time and to introduce 'humanitarian pauses', mainly for the free passage of civilians, evacuation of the sick and wounded and withdrawal of fighters," senior Russian military officer Sergei Rudskoi told a press briefing in Moscow.
The ceasefire would run from 0800 to 1600 local time (0500 GMT to 1300 GMT) "in the area of Aleppo", Rudskoi said.
"During this period the Russian air force and Syrian government troops will halt air strikes and firing from any other types of weapons."
Russia's announcement, to which there was no immediate reaction from rebels, came as the EU condemned the ferocious air war waged on Aleppo over the past three weeks.
"Since the beginning of the offensive by the regime and its allies, notably Russia, the intensity and scale of the aerial bombardment of eastern Aleppo is clearly disproportionate," EU foreign ministers said in Luxembourg.
"The deliberate targeting of hospitals, medical personnel, schools and essential infrastructure, as well as the use of barrel bombs, cluster bombs, and chemical weapons, constitute a catastrophic escalation of the conflict... and may amount to war crimes," they said in a statement.
The EU ministers said they would also press ahead with extending sanctions against Syrian President Bashar al-Assad's regime, but stopped short of threatening measures against Russia.
EU foreign affairs chief Federica Mogherini called Moscow's announcement "positive" but not long enough to allow humanitarian aid to reach the besieged city.
"It can be a start... for sure it is a positive step," she told reporters at the close of the ministerial meeting in Luxembourg.
"The latest assessment from the aid agencies (however) is that 12 hours is needed so work is needed to find common ground," she added.
UN spokesman Stephane Dujarric also welcomed the truce announcement but stressed the "need for a longer pause in order to get the aid in".
Once Syria's thriving commercial hub, Aleppo has been ravaged by air raids and intensifying clashes as regime forces fight to capture the rebel-held east.
Russian air support for the onslaught -- which has destroyed hospitals and other civilian infrastructure -- has spurred the accusations of potential war crimes.
Monday's air strikes on Aleppo killed 13 civilians in the rebel-held district of Marjeh, including 12 members of the same family, said the Syrian Observatory for Human Rights.
"Nine of the family members were minors, including a 17-year-old girl and her newborn," said the Britain-based group's head Rami Abdel Rahman.
The deaths brought to 47 the number of people killed since Sunday morning in east Aleppo, the Observatory said.
The deadliest raids were overnight on a residential block in Qaterji, where the Observatory said Russian strikes killed 18 civilians.
"There are still families under the ruins. We pulled out seven or eight bodies and dozens of wounded," said ambulance driver Abu Mohamed.
"The hospitals are full of casualties. It's a disaster."
More than 430 people have been killed in bombardment on the eastern half since the assault on Aleppo was announced on September 22, according to the Observatory.
Another 82 people have died in rebel fire on government-held neighbourhoods in the west.
Further west in Aleppo province, Russian raids killed 23 people in the village of Uwaijal on Monday, said the Observatory.
US Secretary of State John Kerry met his counterparts from Russia, Iran, and Syria's neighbours in Switzerland on Saturday, and travelled on to London for meetings with the British and other European foreign ministers.
Kerry said the Lausanne meeting produced new ideas on reviving a Syrian truce, after a ceasefire jointly brokered by Moscow and Washington broke down last month, but said high-level contacts to flesh them out would continue Monday.
Syria's war has devolved from a widespread protest movement against Assad's rule to a multi-front war between rebels, jihadists, Kurds and regime forces.
Turkish-backed rebels dealt a major symbolic blow to the Islamic State jihadist group on Sunday by overrunning the northern Syrian town of Dabiq.
Across the border in Iraq, Prime Minister Haider al-Abadi announced the launch Monday of a long-awaited operation to recapture Mosul -- IS's last major stronghold in the country.
In June 2014, IS declared a self-styled Islamic "caliphate" in territory straddling Syria and Iraq.