Moscow has said it will carry out an eight-hour ceasefire to Russian and Syrian government air raids in and around Aleppo, in which at least 35 people were killed on Monday, according to a monitoring group.
The "humanitarian pause" is intended to allow safe passage for civilians and the withdrawal of "militants" from rebel-held eastern Aleppo, General Sergei Rudskoi of the Russian General Staff said in comments quoted by the official TASS news agency.
The Syrian Observatory for Human Rights said at least 23 people were killed in the village of Ouwayjel west of Aleppo, and 12 died in strikes on the rebel-held eastern sector of the divided city.
Activists in Ouwayjel and Aleppo said they believed Russian warplanes had carried out the raids in both locations.
Ibrahim al-Hajj, a spokesman for the White Helmets rescue group in besieged eastern Aleppo, told dpa that the raids were conducted by Russian planes using "new bombs which we called earthquakes due to the loud bangs and massive damage they make."
Al-Hajj put the toll of the eastern Aleppo strikes at 14, including eight children.
Hours after the strikes, Russia announced that its air force and allied Syrian forces would cease fire in Aleppo from 8:00 am to 4:00 pm Moscow time (0500 to 1300 GMT) on Thursday.
Russia has previously announced the creation of safe passages from eastern Aleppo, but only a very small number of civilians are thought to have taken advantage of them.
After a meeting of the UN Security Council in New York, Russian UN ambassador Vitaly Churkin told reporters that Russia's declaration of an 8-hour pause was a unilateral action and having a longer cessation of hostilities would require "some kind of a mutual arrangement."
Churkin said that al-Nusra Front, a UN-designated terrorist group fighting alongside moderate Syrian rebels, has previous taken advantage of humanitarian pauses and noted that terrorists would need to leave Aleppo before the Syrian government and rebels can enter into a ceasefire.
"If there is a broader arrangement ... when Nusra is taken out of the picture, it would be an indefinite ceasefire," he said.
Churkin added that based on an agreement reached over the weekend in Lausanne, Switzerland, the US, Russia and regional stakeholders Saudi Arabia, Qatar and Turkey were supposed to have started work on Monday to separate moderate opposition from al-Nusra.
Reacting to the latest Russian proposal, a spokesman for UN chief Ban Ki-moon said any pause "that's actually implemented" would be very welcome.
"We will use whatever pause we have to do whatever we can, obviously, there is a need for longer pause in order to get trucks rolling in," Stephane Dujarric said.
"We have been calling for at least a 48-hour ceasefire ... in order to get humanitarian aid in."
The UN has previously said security concerns and fears of arrest prevent Aleppo's civilians from crossing at government-designated safe passages, noting that Syrian army units are stationed at them.
In August UN humanitarian chief Stephen O'Brien slammed a deal that saw rebels and civilians evacuated en masse from the besieged Damascus suburb of Daraya before government forces moved in.
Such agreements were contrary to international humanitarian law and human rights law and should not be a precedent for other besieged areas of Syria, O'Brien said.children, have been killed in and around Aleppo since a brief ceasefire collapsed on September 19.
The majority of deaths were in rebel-held eastern Aleppo, a total of 448 civilians, the Observatory said. The government-held western sector has also been repeatedly targeted by indiscriminate rebel shelling.
Russia intervened in Syria a year ago to prop up President Bashar al-Assad's crumbling army.Its air campaign has enabled government forces to reclaim territory from both rebels and the Islamic State extremist group.