Syria's revolution forces lost all of the northern neighborhoods of their stronghold in east Aleppo on Monday, as the regime 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 regime or Kurdish forces, others heading south into areas still under opposition control.

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

"There is mass displacement and morale is in the gutter," he said, his voice cracking with emotion.

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

UN humanitarian envoy Stephen O'Brien said on Tuesday initial reports indicated that up to 16,000 people have been displaced by fighting in the city over the past few days.

"The parties to the conflict in Syria have shown time and again that they are willing to take action to secure military advantage even if it means killing, maiming or starving civilians into submission in the process."

The revolution forces have steadily lost territory since Russia intervened to bolster Bashar al-Assad in September 2015.

On Monday, regime forces seized the Sakhour, Haydariya and Sheikh Khodr districts, and Kurdish fighters took the Sheikh Fares neighborhood from revolution fprces, the UK-based Syrian Observatory for Human Rights monitor said.

Hungry civilians

The Syrian Civil Defense group, known as the 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.

Nearly 10,000 civilians have fled the east, the Observatory said late on Sunday, with about 6,000 moving to the Kurdish-held Sheikh Maqsoud neighborhood and 4,000 to regime-held west Aleppo.

Kurdish officials published a video they said showed civilians crossing a field to Sheikh Maqsoud, where local forces helped people cross a makeshift barrier.

Hundreds of civilians were also fleeing south to the remaining districts with little more than the clothes they were wearing.

People in southern neighborhoods were donating blankets and other items to the new arrivals, who had travelled on foot, exhausted, cold and hungry.

The United Nations said it was "deeply concerned" about civilians in the east, where international aid is exhausted and food stocks are desperately low.

The UN has appealed for access to the east many times, but has failed to secure the necessary guarantees to enable aid deliveries.

"In terms of east Aleppo, we just need the green light from the people who control the roads going in because, as you know, the east of Aleppo is besieged," said Ramesh Rajasingham, the UN's deputy regional humanitarian coordinator for the Syria crisis.

PHOTO CAPTION

Civil defense members and men inspect a site damaged after an airstrike in the besieged al-Qaterji neighborhood of Aleppo, Syria October 11, 2016. REUTERS

Al-Jazeera