DAMASCUS/ISTANBUL - Syrian authorities have accused rebel fighters of executing 21 civilians, including women and children, at close range as they quit second city Aleppo last week, state media reported.

The bodies were found in two neighbourhoods in east Aleppo, state news agency SANA said late Sunday.

The head of Aleppo's forensic unit Zaher Hajjo told SANA that "21 corpses of civilian victims, including five children and four women, killed by terrorist groups" were examined.

"The bodies were found in prisons run by the terrorist groups in Sukkari and al-Kalasseh, and they were found to have been executed by gunshot at very close range," Hajjo was quoted as saying.

Under a landmark deal brokered by regime ally Russia and rebel backer Turkey, 35,000 rebels and civilians left the former opposition stronghold of east Aleppo last week.

Days before the evacuations began, the UN said it had received credible reports of at least 82 civilians, including 11 women and 13 children, being executed by pro-government forces in Aleppo.

On Monday, the Russian defence ministry said "dozens of Syrians" were summarily executed in east Aleppo by rebels. "Mass graves containing dozens of Syrians who were summarily executed and subjected to savage torture have been discovered," spokesman Igor Konachenkov said, according to Russian agencies.

Meanwhile, the Turkish army on Monday accused Islamic State (IS) militants of killing at least 30 civilians seeking to flee the flashpoint Syrian town of Al-Bab which Ankara and its rebel allies have been seeking to capture for weeks.

The army said that the civilians were killed with mines and homemade bombs as they tried to make their way out of Al-Bab, the state-run Anadolu news agency reported, without giving further details.

Turkish forces and allied Syrian rebels have been seeking to take Al-Bab as a key part of un unprecedented four month campaign that began in late August. But they have been facing tough opposition from the militants and suffered the highest casualties of the campaign so far in the fight for the town.

Turkey at the weekend deployed more tanks and artillery to the border and also as sent 500 elite commandos to Al-Bab in readiness for a final fight for the town, reports said. Thirty-six Turkish soldiers have died so far in the operation - dubbed Euphrates Shield - after another wounded soldier lost his life in hospital in Turkey overnight, reports said. Sixteen Turkish soldiers were killed by IS in the battle for the town on Wednesday - Ankara's biggest loss so far since it launched its incursion.

A Britain-based monitoring group has accused Turkey of killing 88 civilians in air strikes on Al-Bab, including 21 children. However the army has unequivocally denied such claims.

President Recep Tayyip Erdogan said at the weekend the battle for Al-Bab is nearly finished, reiterating Turkish forces would then head to Manbij, a former bastion of IS that is now under the control of US-backed, Kurdish-led militia.

Turkey on Monday said it wanted international air support for its army's assault on the militant-held Syrian town of Al Bab where the military is facing tough resistance from Islamic State (IS) extremists.

Turkish forces have for weeks joined pro-Ankara Syrian rebels in fierce fighting for Al Bab, taking increasing casualties as they approach closer to the centre. Turkey is part of the US-led coalition against IS militants in Syria and lets Western war planes use its Incirlik air base as a hub for air raids.

"As for our operations in Al Bab, the international coalition should assume its responsibilities, especially where air support is concerned," presidential spokesman Ibrahim Kalin said in televised comments in Ankara.

"The weather conditions can sometimes entail delays," Kalin acknowledged. "But the absence of air support when there is no valid reason is unacceptable," he added.

The US and its allies have been conducting their own air strikes against IS targets in Syria but there have been no reports of them specifically aiding the Turkish operation.

Turkey at the weekend deployed more tanks and artillery to the border and also has sent 500 elite commandos to Al Bab in readiness for a final fight for the town, reports said.

A Britain-based monitoring group has accused Turkey of killing 88 civilians in air strikes on Al-Bab. However the army has unequivocally denied such claims.

Thirty-six Turkish soldiers have died so far in the operation inside Syria - dubbed Euphrates Shield - since it was launched on August 24.

Islamic State militants last week circulated a video purportedly showing two Turkish soldiers captured by the extremists in Syria being burned alive.

The authenticity of the video cannot be confirmed and Turkey's leadership has made no mention of the images.

Turkey's Defence Minister Fikri Isik has said three Turkish soldiers are being held by IS, without giving further detail. The issue was evoked at Kalin's televised news conference but the spokesman did not give any comment.

Users in Turkey had reported severe problems with social media after the video emerged. However by Monday access to Twitter was fully restored after three days of disruption.