Evacuations of embattled eastern Aleppo, which began Thursday after days of efforts to negotiate a cease-fire, have come to a halt.
Thousands of civilians and fighters have already been evacuated from the rebel-held enclave: Some 3,000 civilians were evacuated in the first few convoys, along with more than 40 wounded people, the International Committee of the Red Cross said Thursday.
The aid group anticipated it would take days to fully evacuate east Aleppo.
But on Friday, efforts were halted, NPR's Alison Meuse reports.
"The World Health Organization Syria representative Elizabeth Hoff says her staff were told to leave the evacuation area south of the city 'without explanation.' Hoff is in Aleppo and was addressing reporters at a news conference in Geneva," Alison says.
At one point on Friday, a witness to the evacuations told Reuters that a convoy had "ground to a halt" on the road out of eastern Aleppo, with people packed onto flatbed trucks exposed to the elements.
The weather in Aleppo on Friday morning hovered around freezing, according to reporter Louisa Loveluck.
Reuters reports that there are "recriminations on all sides," with various explanations for why evacuations have stopped:
"Rebel sources accused pro-government Shi'ite militias of opening fire on bus convoys taking evacuees out of the city.
"A Syrian official source said the evacuation was halted because rebels had sought to take out people they had abducted with them, and they had also tried to take weapons hidden in bags. This was denied by Aleppo-based rebel groups.
"But a media outlet run by the pro-government Hezbollah group said protesters had blocked the road from the city, demanding that wounded people from the villages of Foua and Kefraya in nearby Idlib province should also be evacuated.
"It also said rebels had bombarded a road due to be used by buses to conduct the evacuation from the Shi'ite villages."
Earlier in the week, Turkey and Russia negotiated a cease-fire that collapsed before evacuations could begin.
The Associated Press and Reuters have reported that disputes over Foua and Kefraya were a main reason for the failure of that deal: The wire services say Iranian-backed militias allied with the regime interfered with the truce to demand the evacuation of the two villages. The demands appeared to be met, with convoys headed to the two villages as evacuations began in Aleppo.
There are conflicting claims over how many people have been evacuated so far from eastern Aleppo, and how many remain.
"Russia is claiming that all women and children have been taken out of eastern Aleppo and that a final sweep by the Syrian military is underway to clear out the last remaining rebels in the city — though there is no evidence on the ground of this," the AP reports. "A statement on Friday from the Russian military's Center for Reconciliation in Syria says the evacuations have been 'completed.' "
Aid groups and the U.N. deny that Russian claim, saying many people remain in need of evacuation.