The final phase of the evacuation of rebel-held eastern districts of the Syrian city of Aleppo has restarted, after being stalled for a day.

Syrian state TV broadcast pictures of buses leaving the rebel enclave and entering a government-controlled area.

A UN official also told Reuters news agency that the evacuation had resumed.

Activists said 60 buses were stuck in the rebel enclave overnight, forcing 3,000 people to wait in freezing weather with little to eat or drink.

Reasons for the hold-up were not clear. But state media blamed rebels in neighbouring Idlib province, accusing them of preventing the simultaneous evacuation of two pro-government Shia towns there.

After waiting more than a day, the first five buses in the convoy left the rebel enclave and crossed into government-held Ramousseh on Wednesday afternoon.

By late in the evening, the Syrian Observatory for Human Rights, a UK-based group that monitors the civil war, was reporting that all rebel fighters had left the eastern districts, putting the city under the full control of the Syrian government.

However, representatives from the UN and the US state department told Reuters this was not yet confirmed.

The official Sana news agency said the evacuation buses were heading to the countryside west of Aleppo under the supervision of the Syrian Arab Red Crescent and the International Committee of the Red Cross.

At the same time, four buses and two ambulances carrying wounded and sick people had been allowed to leave the two towns in Idlib besieged by rebel forces, Foah and Kefraya, it added.

Sana also cited its sources as saying that 21 bus drivers had been freed after being "held by terrorists" while on their way to the towns on Tuesday evening.

There was no immediate comment from rebel officials. However, the Syrian Observatory did report earlier that 21 buses had been unable to enter Foah and Kefraya.

It is not clear how many civilians and rebel fighters are still inside the rebel enclave.

The UN estimated last Thursday that there were 50,000 people there.

On Tuesday, the ICRC said 25,000 people had been evacuated since the operation began a week ago, but the Syrian Observatory said the total was closer to 17,000.

If this is the last convoy to leave Aleppo, Wednesday could be the day the whole of the city returns to government control, says the BBC's James Longman in Beirut.

The Syrian army seems determined to clear the rebel enclave, he adds, and has been broadcasting announcements via loudspeaker, calling on the last fighters to leave before soldiers arrive.

But a spokesman for the Fastaqim rebel group, Ward Furati, told the Associated Press they "won't leave until security of all the civilians has been fully guaranteed".

Aleppo was once Syria's largest city, and its commercial and industrial hub before the uprising against President Bashar al-Assad began in 2011.

For much of the past four years it was divided roughly in two, with the government controlling the western half and rebels the east.

Troops finally broke the deadlock this year with the help of Iranian-backed militias and Russian air strikes, reinstating a siege on the east in early September.

After breaking through the rebels' defensive lines in mid-November, they quickly advanced and had seized all but 2.6 sq km (1 sq mile) by the time a ceasefire was brokered by Russia and Turkey, which backs the opposition to Mr Assad.