Rescuers say at least 100 people have been killed in a bomb blast apparently targeting civilians trying to escape from fighting around Aleppo.

The explosion ripped through a bus depot full of people waiting to evacuate from rebel-held areas in northern Syria.

Buses waiting to transport civilians to government territory had been parked for more than 30 hours as a much-criticised population transfer deal stalled.

Members of the White Helmets rebel rescue service said they had already pulled at least 100 bodies from the rubble.

State TV showed horrific images of bodies strewn on the ground and near buses.

A senior rebel official said 20 rebels who guarded the buses were killed as well as dozens of passengers.

The government and rebels disagreed over the number of gunmen to be evacuated, leaving the buses stuck.

The blast happened after thousands of Syrians being evacuated from their besieged towns had spent the night on buses at an exchange point.

Ahmed Afandar, a resident evacuated from his home town near Madaya, said dozens of buses carrying women, children and men were not being allowed to proceed toward rebel-held Idlib as planned.

"The people are restless and the situation is disastrous," said Mr Afandar. "All these thousands of people are stuck in less than half a kilometre (500 yards)."

He said the area was walled off from all sides and there were no toilets.

Syrian State TV said the evacuation had now started to resume

Reports of the attack have been met with horror and criticism internationally.

Tobias Ellwood, the Foreign Office Minister for the Middle East, said he was "appalled" to hear civilians had been attacked.