A ceasefire was struck with government forces on Tuesday.
Plans to evacuate besieged rebel districts of Aleppo were under threat on Wednesday as renewed air strikes and shelling rocked the city.
Iran, one of Syrian President Bashar al-Assad's main backers in the battle that has all but ended four years of rebel resistance in the city, imposed new conditions, saying it wanted the simultaneous evacuation of wounded from two villages besieged by rebel fighters, according to rebel and U.N. sources.
There was no sign of that happening. Insurgents fired shells at the two majority Shi'ite villages, Foua and Kefraya, in Idlib province west of Aleppo, causing some casualties, the British-based Syrian Observatory for Human Rights said.
There was no immediate indication when the evacuation might take place but a pro-opposition TV station said it could be delayed until Thursday.
A ceasefire brokered on Tuesday by Russia, Assad's most powerful ally, and Turkey was intended to end years of fighting in the city, giving the Syrian leader his biggest victory in more than five years of war.
But air strikes, shelling and gunfire erupted on Wednesday and Turkey accused government forces of breaking the truce. Syrian state television said rebel shelling had killed six people.
Russian Foreign Minister Sergei Lavrov predicted however that rebel resistance would last no more than two or three days. The defence ministry in Moscow said the rebels now controlled an enclave of only 2.5 square km (1 square mile).
Turkey was in contact with Iran, Russia and the United States to try and ensure the evacuation of civilians and rebel fighters from Aleppo.
Officials in the military alliance backing Assad could not be reached immediately for comment on why the evacuation, expected to start in the early hours of Wednesday, had stalled.
Nobody had left by dawn under the plan, according to a Reuters witness waiting at the departure point, where 20 buses stood with engines running but showed no sign of moving into rebel districts.
People in eastern Aleppo packed their bags and burned personal belongings, fearing looting by the Syrian army and its Iranian-backed militia allies.
U.N. war crimes investigators said the Syrian government bore the main responsibility for preventing any attacks and reprisals in eastern Aleppo and that it must hold to account any troops or allied forces committing violations.
In what appeared to be a separate development from the planned evacuation, the Russian defence ministry said 6,000 civilians and 366 fighters had left rebel-held districts over the past 24 hours.
A total of 15,000 people, including 4,000 rebel fighters, wanted to leave Aleppo, according to a media unit run by the Syrian government's ally Hezbollah.
(Reuters)
1. The smoke after the fire
)
Air strikes and smoke rising from residential areas is a everyday phenomenon.
(Photo: Reuters)
2. Divided support
)
Protesters burn a picture of Russian President Vladimir Putin, against Russia's support of the Syrian regime.
(Source: Reuters)
3. Will the ceasefire save Aleppo?
)
Protesters in London show solidarity with Aleppo.
(Source: AFP)
4. Reflection of the past
)
People wave Turkish and Free Syrian flags as an aid convoy to Aleppo is about to leave.
(Source: AFP)
5. Struggling for survival
)
Evacuated Syrians fight for food aid in government-controlled Jibreen area in Aleppo.
(Source: Reuters)
6. Bashar al-Assad's regime
)
This picture from 2013 is of a police academy in Aleppo, after it was captured by Free Syrian Army fighters, wherein Syria's President Bashar al-Assad picture is riddled with holes.
(Source: Reuters)
7. What lies ahead?
)
Men evacuated from eastern districts of Aleppo being prepared to begin their military service at a police centre in Aleppo.
(Source: Reuters)
8. All that was lost...
)
Free Syrian Army fighter carries a body of a fellow fighter.
(Source: Reuters)
9. Holding on
)
This picture was taken in 2012, wherein a boy is holding pita bread while other still have to wait for their 'daily bread'.
(Source: Reuters)
10. Ghosts of the past still continue to haunt...
)
A picture that went viral earlier this year, of a four-year-old Syrian boy Omran who was rescued from the rubble, covered covered in dust and blood.
(Source: AFP)
11. Fleeing the mahem
)
Syrian men carrying babies make their way through the rubble in Salihin neighbourhood of the northern city of Aleppo.
(Source: AFP)
12. Bleeding hearts
)
White Helmets, Syrian civil defence volunteers, rescue a boy from rubble following a barrel bomb attack in Bab al-Nairab.
(Source: AFP)
