The United Nations called on Tuesday for full access to civilians inside and outside of Syria's eastern Ghouta to meet their urgent needs, after some 50,000 have fled in recent days.

Another 104,000 are estimated to have been uprooted by fighting around the northern town of Afrin, where 10,000 are stranded nearby trying to cross into areas controlled by the Syrian government, the UN refugee agency said.

"The UNHCR, the UN refugee agency, is alarmed at a further deepening of the humanitarian crisis in Syria as fierce fighting in eastern Ghouta, rural Damascus and Afrin causes massive new displacement," UNHCR spokesman Andrej Mahecic told a Geneva briefing. "These people left with nothing and they need esentially everything from clothes to shelter."

About 70 per cent of the 50,000 evacuated from eastern Ghouta are women and children and many children are suffering diarrhoea and respiratory ailments which can be deadly, as well as scabies and lice, UNICEF spokeswoman Marixie Mercado said.

UNICEF estimates that about 100,000 people are still inside Afrin district, half of whom are children, she added.

In the meantime, Islamic State fighters holding a small district in Damascus have gained some ground after driving out Syrian army units that moved into a neighbouring area that rebels abandoned last week, a war monitor said.

A Syrian soldier secures aid convoy after its return from eastern Ghouta in Damascus

In fighting that lasted 24 hours, the ultra-hardline militant group killed 36 Syrian soldiers, the British-based Syrian Observatory for Human Rights said. The Syrian army could not immediately be reached for comment.

The district of al-Qadam lies in the Syrian capital's southern suburbs and has not been part of the month-long offensive waged by the army against rebels in eastern Ghouta.

Islamic State has lost almost all its territory in Syria after two rival offensives last year by the Syrian army, backed by Russia and Iran, and an alliance of Kurdish and Arab militias backed by the United States.

It now controls only the small pocket in Qadam, a patch of territory in southwest Syria near the borders with Jordan and Israel, and two small areas of desert on each side of the Euphrates near the border with Iraq.