BEIRUT -- Thousands of Syrian civilians fled fierce fighting in eastern Aleppo on Sunday as government forces moved to slice the city's last rebel-held stronghold in half.
Rebel defenses collapsed as government forces pushed into the city's Sakhour neighborhood, coming within about a half-mile of commanding a corridor in eastern Aleppo for the first time since rebels swept into the city in 2012, according to Syrian state media and the Britain-based Syrian Observatory for Human Rights monitoring group.
Kurdish-led forces operating autonomously of the rebels and the government seized the Bustan al-Basha neighborhood, allowing thousands of civilians to flee the decimated district to the predominantly Kurdish Sheikh Maqsoud, in the city's north, according to Ahmad Hiso Araj, an official with the Syrian Democratic Forces.
The government's push -- backed by thousands of Shiite militia fighters from Lebanon, Iraq, and Iran, and under the occasional cover of the Russian airstrikes -- has laid waste to Aleppo's eastern neighborhoods.
At least 500 people have been killed and more than 1,000 wounded in a 13-day offensive led by President Bashar al-Assad's troops on the east side of the city.
An estimated quarter-million people have been trapped in wretched conditions in the city's rebel-held eastern districts since the government's siege of the enclave in late August. Food supplies are running perilously low, the U.N. warned Thursday, and a relentless air assault by Syrian government forces has damaged or destroyed every hospital in the area.
"The situation in besieged Aleppo [is] very very bad, thousands of eastern residents are moving to the western side of the city," said Khaled Khatib, a photographer for the Syrian Civil Defense search-and-rescue group, also known as the White Helmets.
"Aleppo is going to die," he posted on Twitter.
It was unclear Sunday how long rebel forces could hold out in the final district connecting their territory north to south. "We are in the process of repelling the onslaught and fortifying our defense lines," said Yasser al-Youssef, a spokesman for the Nour al-Din al-Zinki Brigade, one of the rebel groups.
"All I can see is Assad's forces advancing. People have been running all day. It's chaos," said Ismail Abdullah, a volunteer with the White Helmets.
The Syrian Observatory, which monitors the conflict through a network of local contacts, said around 1,700 civilians had escaped to government-controlled areas and another 2,500 escaped to Kurdish authorities. Wissam Zarqa, an English teacher in eastern Aleppo and an outspoken government opponent, said some families would stay put in the face of advancing government forces.
Syrian state media reported government forces had seized the Jabal Badro neighborhood and entered Sakhour on Sunday after the government took control of the Masaken Hanano neighborhood Saturday.
Masaken Hanano had been the largest rebel-held district of Aleppo, the city that was formerly Syria's largest city and commerce capital. The neighborhood was the first to slip from government control. Its fall underscored how far the tide has turned in favor of Assad's forces, 5½ years into a war that has killed a half million people and displaced most of Syria's prewar population.
On Syrian state television, families were seen waiting for green buses to leave for government-held areas. Ragged from exhaustion, some carried the young and the elderly on their shoulders. Their destination was unknown.
Syrian state TV had earlier broadcast a video showing a teary reunion between a soldier and his family after nearly five years apart. The report said the family had been trapped in Masaken Hanano.
The Lebanese Al-Manar TV channel reported from the neighborhood Sunday morning, showing workers and soldiers clearing debris against a backdrop of bombed-out buildings on both sides of a wide thoroughfare. Al-Manar is operated by Hezbollah, the Lebanese militant group aligned with the Syrian government.
The Kurdish-led Syrian Democratic Forces' advance into Bustan al-Basha dealt the opposition a further blow.
Rebels and opposition figures have long accused the Syrian Democratic Forces and its predecessor groups of conspiring with the government to quash a nationwide revolt.
Araj denied there was any coordination between government and Kurdish-led forces.
"We were responding to calls from residents in Bustan al-Basha to secure the neighborhood," he said. He added that the Syrian Democratic Forces had entered the area handily as rebel militants fled.
Turkish news agency Anadolu also reported Sunday that the Islamic State extremist group had used chemical weapons against Turkish-backed Syrian opposition fighters in northern Syria, wounding 22. The report cited a statement by the chief of general staff's office. The report could not be immediately verified independently.
Later Sunday, Turkey's emergency relief directorate, which investigated the claim, said it found no trace of chemical warfare. The military was not available for further comment.
Information for this article was contributed by Philip Issa and Cinar Kiper of The Associated Press; and by Louisa Loveluck of The Washington Post.
A Section on 11/28/2016