The Syrian army has ordered rebels in Aleppo to leave the city or face "inevitable death", as a series of air strikes on the neighbouring Idlib province killed at least 50 people, including several children.
Aleppo shook from the sound of explosions throughout the day as pro-government forces, including foreign fighters dispatched from Lebanon, Iraq and Iran, pounded the city's opposition neighbourhoods in the east.
Rebel defences have buckled after months of siege and waves of devastating air strikes, and the opposition could soon be driven from Syria's largest city.
It would mark their biggest defeat since 2011, when a government crackdown against dissent sparked a civil war.
Rebels swept into Aleppo in 2012.
The government's fortunes changed after the Russian air force intervened in September 2015, allowing the government to begin to reconquer it.
Army spokesman Brigadier General Samir Suleiman said government forces would "continue fighting until they restore stability and security to all neighbourhoods".
He said the army has already retaken more than half the neighbourhoods in eastern Aleppo, and that special forces would lead the battle in the narrow streets of the city's historic district.
On Sunday, the government captured large swathes of the Qaterji, Maysar and Karm al-Turab neighbourhoods, bringing their eastern flank to within less than a kilometre (half a mile) of the citadel that anchors the centre of the city. The citadel has remained under government control throughout the conflict.
The advance also threatens to split the rebels' rump enclave in two and isolate the once densely populated al-Shaar neighbourhood.
Judy al-Halaby, an activist still in the city, said residents began evacuating the area five days ago, with thousands fleeing to government control and thousands of others deeper into rebel territory.
The UN estimates that more than 31,000 people have fled their homes since pro-government forces began advancing inside east Aleppo one week ago.
In the Hanano district, which was captured by government forces on November 26, hundreds of people were seen returning to their homes, as minivans passed through carrying troops and militiamen to the front lines.
For some of the residents, it was their first time seeing their homes in years.
Mohammed Qadra, 58, who left the district four years ago, returned from the government-held western part of the city on Sunday to discover that his home was so badly damaged that it is impossible for him to return.
"I have no money to renovate it now but I will do so step by step," said the man, who said he cried once he saw his home.
Russian or government jets, meanwhile, were thought to be behind several raids on Idlib province on Sunday, including two that struck rural markets and killed dozens of people, activists said.
The Syrian civil defence first responder group said 52 civilians were killed in raids across the province.
"The fear was clear on everyone's face. There were limbs and bodies all over the ground," said Ahmad al-Sheikho, of the civil defence, who said he arrived at the Maaret al-Nouman marketplace 10 minutes after it was struck.
The Britain-based Syrian Observatory for Human Rights monitoring group said six members of the same family died in the attack.
The market at Kafranbel, a village 11 kilometres (seven miles) away, was also bombed a few hours earlier.
The observatory said 26 people, including members of the local religious police force, were killed.
Four children and two women were killed in Tamanaah when the village was attacked by government helicopters, the observatory and civil defence reported.
Russia's military said last month it was resuming air strikes on the north-western Idlib province, where Kafranbel is located, and in the central Homs province in support of government forces.
Kafranbel is at least 12 kilometres (seven miles) from the nearest front line, at Jabal Zawiyeh.