Damaged buildings at Zabadani
Damaged buildings at ZabadaniReuters

The UN began evacuating hundreds of wounded people from besieged Syrian towns Wednesday in a rare sign of humanitarian progress amid faltered peace talks and a fraying ceasefire.

The UN secured the evacuation of dozens of people needing medical attention from four besieged towns as part of a complex humanitarian mission, according to the AFP news agency.

"Plans are underway to evacuate some 500 people including the sick, wounded and their family members" from four besieged towns "in urgent need of life-saving medical attention," said UN spokesman Stephane Dujarric.

On the outskirts of the rebel-held town of Madaya, seven large white buses carrying evacuated residents stopped along a route lined by shrubbery.

Dozens of men, women and children got out of the bus and were checked by security officials before boarding once more, according to AFP.

A similar operation had occurred earlier outside nearby Zabadani, where 25 men were transported out of the town.

The simultaneous evacuations were taking place Wednesday from rebel-held Zabadani and Madaya near Damascus, and the government-held towns of Fuaa and Kafraya in northwest Idlib province.

Madaya shot to infamy in December 2015 when dozens of residents starved to death.

Aid deliveries to the four localities always occur simultaneously and in equal amounts, and a similar stipulation applied on Wednesday for those being evacuated.

More than four million in Syria live in besieged or hard-to-reach areas, with limited or no access to food or medical supplies.

The UN has long pressed Damascus to grant unrestricted access to these areas, and has asked all sides to end besiegement.

Despite fierce criticism, the regime frequently denies passage to aid convoys or limits what kind of assistance can enter.

The dire humanitarian situation has played a major role in the opposition walking away from the troubled peace talks in Geneva.

An already-shaky ceasefire between the government and non-jihadist rebels was severely strained on Tuesday after at least 44 people were killed in air strikes on two markets in northwest Syria.

The deaths of 37 civilians in a market in the city of Maaret al-Numan and another seven killed in nearby Kafranbel were some of the deadliest attacks since the truce took hold on February 27.

AFP contributed to this report.