The Syrian army and its allies announced the capture of a swath of eastern Aleppo from rebels on Monday in an accelerating attack that threatens to crush the opposition in its most important urban stronghold.
Rebels denied that the army had taken the strategically vital Sakhour area which – if it fell – would mean rebel-held territory in the eastern part of the city was split in two.
But the Syrian Observatory for Human Rights said the government had taken Sakhour, and rebels had lost control of more than a third of eastern Aleppo in recent days.
Thousands of residents were reported to have fled. A rebel fighter reached by Reuters said there was "extreme, extreme, extreme pressure" on the insurgents there.
Capturing eastern Aleppo would be the biggest victory for President Bashar Assad since the start of the uprising against him in 2011, giving him control of the whole city.
For Assad, taking back Aleppo would shore up his grip over the main urban centres of western Syria where he and his allies have focused their firepower even as much of the rest of the country has slipped from their grip.
It would also be seen as a victory for his allies, Russia and Iran, which have outmaneuvered the West and Assad's regional enemies through direct military intervention.
With military backing from the Russian air force, Iran, and Lebanon's Hezbollah, Assad has gradually closed in on eastern Aleppo this year.
Citing a military source, Syrian state TV said the army and its allies had seized the entire Sakhour area and were working to clear it of mines. Backed by allied militiamen, the army has been advancing into eastern Aleppo from the northeast in recent days, and made significant gains over the weekend.
A military news service run by Hezbollah declared the northern portion of eastern Aleppo was now under government control. Observatory director Rami Abdulrahman called it the biggest defeat for the opposition in Aleppo since 2012.
Abdulrahman said part of the area had been seized by the Kurdish YPG militia, which is hostile to the rebels in eastern Aleppo and had advanced into the rebel-held territory from the Kurdish-controlled Sheikh Maqsoud district.
Damascus and its allies have steadily closed in on rebel-held eastern Aleppo this year, first cutting off the most direct route to nearby Turkey before encircling it from the west and then beginning a fierce assault in September.
While some of the rebels in Aleppo have received support from states such as Turkey, Saudi Arabia, Qatar and the United States during the war, they say their foreign backers have failed them as Assad and his allies unleash enormous firepower.
"There is great, great pressure on the fighters in Aleppo and there is very ferocious shelling and heavy attrition of people and ammunition," said the rebel fighter. "God willing the fighters will hold on and be able to resist the regime."
The fighting has forced thousands of residents of eastern Aleppo to flee. Some have gone to the Kurdish-held Sheikh Maqsoud district, others have gone over to government territory, and others have moved deeper into remaining rebel-held areas.
Mohammad Sandeh, a member of the opposition city council of Aleppo, told Reuters that many people were on the move but staying in the remaining rebel-held parts of Aleppo.
"The bombardment is still heavy. There's big displacement from the eastern neighborhoods. They are going towards the areas that are somewhat further [from the front lines]," he said.
"There's fear that the regime will advance more."
Saleh Muslim, joint head of the Syrian Kurdish PYD party, told Reuters that between 6,000 to 10,000 people had fled to Sheikh Maqsoud, where they were being received.
The Observatory said several thousand more had crossed front lines in other parts of eastern Aleppo and had been taken to government-controlled areas of western Aleppo.
A spokesman for the UN refugee agency UNHCR said exact figures for the number of displaced were difficult to gauge.
"But the Syrian Arab Red Crescent on the ground reports that just over 2,000 people have left eastern Aleppo for the government-controlled district of Jibreen," the spokesman said via email.
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