Residents walk through rubble in worn-torn Aleppo
Residents walk through rubble in worn-torn AleppoReuters

Syria's rebels lost all of the northern neighborhoods of their stronghold in east Aleppo on Monday, as the army made significant advances in its offensive to recapture the entire city.

The regime gains have prompted an exodus of thousands of desperate civilians, some fleeing to districts held by the government or Kurdish forces, others heading south into areas still under opposition control.

Figures published on Sunday indicated that nearly 10,000 civilians had fled eastern as the Syrian army advanced.

"The situation is disastrous," Ibrahim Abu Al-Leith, a spokesman for the White Helmets rescue group in the Ansari neighborhood, said on Monday.

"There is mass displacement and morale is in the gutter," he added.

"People are sleeping in the streets. They don't have anything to eat or drink, but neither do we," he told AFP.

The loss of eastern Aleppo would be a potentially devastating blow to Syria's rebels, who seized the area in 2012.

The opposition has steadily lost territory since Russia intervened to bolster President Bashar Al-Assad in September 2015.

On Monday, government forces seized the Sakhur, Haydariya and Sheikh Khodr districts, and Kurdish fighters took the Sheikh Fares neighborhood from rebels, the Syrian Observatory for Human Rights monitor said.

"This is their (the rebels') worst defeat since they seized half the city in 2012," Observatory director Rami Abdel Rahman said.

The advances left all of northeast Aleppo under government control.

Syria's White Helmets warned on Monday they had no more fuel reserves for rescue vehicles.

In a video statement, the group urged "all humanitarian, aid, and medical organizations to immediately intervene to put an end to the humanitarian disaster" facing civilians in besieged Aleppo.

The government assault of heavy air strikes, barrel bomb attacks and artillery fire has killed at least 247 civilians in east Aleppo, according to the Observatory.

Barrel bombs are crude weapons -- containers packed with explosives and scrap metal that are typically dropped from helicopters.

Syrian President Bashar Al-Assad has been accused of using these weapons, but has repeatedly denied the accusations and has claimed in interviews that no such weaponry exists.

Meanwhile, rebel fire into the government-held west has also killed at least 27 civilians, among them 11 children, since November 15, the Observatory said.

Syria's Al-Watan daily, which is close to the government, said the next stage would be "to divide the remaining (rebel-held) area into... districts that will be easily controlled and to capture them successively".

But British Foreign Secretary Boris Johnson called for an immediate ceasefire in Aleppo, saying the assault "is threatening a humanitarian catastrophe".

More than 300,000 people have been killed and millions displaced since the conflict began with anti-government protests in March 2011.

AFP contributed to this report.