BEIRUT — Ambulances with wounded civilians rolled out of the last rebel-held districts in Syria's embattled Aleppo on Thursday, beginning a possible major evacuation effort after earlier failures to ferry out frightened residents and defeated fighters.
But the deal had already been thwarted twice in just 24 hours, underscoring the complex politics dominating Syria's war and the deep stakes over strategic Aleppo - which appeared poised to now fall under full control of Syrian government forces.
Convoys of ambulances and buses were assembled in the rebel zones, but it remained unclear when the large-scale departures could commence. Syrian state TV showed images of ambulances carrying away wounded civilians in what could be the first phase of the evacuations.
Syrian forces and their allies have pushed rebel fighters into a sliver of enclaves after nearly a month of relentless attacks to reclaim control of the strategic city. Winning back full control of Aleppo would be a huge prize for the government of Syrian President Bashar Assad, but a staggering blow to the opposition groups that have fought his regime for more than five years.
The buses arrived as part of a historic exit deal for rebels and civilians. Brokered by Russia and Turkey, the agreement could see the largest evacuation of Syria's conflict. But any flare-up in fighting could once again cause the plan to unravel.
"The buses are there, the ambulances are there, 100 staff are there. The operation is still ongoing," said Ingy Sedky, a spokeswoman for the International Committee of the Red Cross.
A planned evacuation Wednesday was held up by objections from Iran, a key backer of Assad, according to a U.N. official interviewed by Agence France-Presse, and three rebel commanders. And early Thursday, rescue workers and construction workers came under a hail of gunfire as they cleared a road leading to an agreed evacuation point.
Labib Nahas, who represents the Ahrar al-Sham rebel group, blamed the attack on Syrian government troops or Iran-backed militia, saying they had "targeted injured civilians."
The United Nations cited "alarming" reports this week that pro-government militia went house-to-house as they swept through several rebel districts last week, executing civilians.
Nearly 1,000 people have been killed in east Aleppo during the past two weeks, according to the Turkish government. Many have been buried in shallow mass graves, it claims.
The International Committee of the Red Cross said it expected between 200 and 250 wounded people to leave in the first wave of evacuations. The area's hospital network has been ravaged through attacks by Syrian and Russian warplanes. Rebel fighters were expected to leave during the second stage of the evacuation, but questions remained on how they would fare after leaving the city.
Jan Egeland, a U.N. humanitarian adviser, said he was hopeful the plan could still proceed.
Inside the rebel enclave, residents spoke of deep relief.
"You don't understand what we have lived through here. Death hung above us, the world turned their backs," said Mohamed al-Halabi, an electrician whose entire family was killed in an airstrike on his workshop. "Maybe today, finally, they will help us."
The Washington Post's Heba Habib in Stockholm and Brian Murphy in Washington contributed to this report.