More than 1,000 people, mostly women and children, are in urgent need of medical evacuations from the besieged Syrian enclave of Eastern Ghouta, the United Nations said on Monday.

Rebel-held parts of Ghouta are under a crippling government siege that has made food and medicine difficult to access for its estimated 400,000 residents.

"There are more than 1,000 people who require medical evacuations. The majority of them are women and children," said Linda Tom, from the UN's humanitarian coordination office (OCHA) in Damascus.

According to numbers provided on Monday by OCHA, they include more than 77 "priority cases".

Since February 18, Syrian troops have been waging a fierce offensive on rebels in Eastern Ghouta, the last opposition bastion on the outskirts of Damascus.

OCHA said 28 health facilities in Eastern Ghouta had been hit in the assault, and nine health workers killed.

Rebels have also fired rockets onto the capital.

According to OCHA, five hospitals and 26 schools in Damascus have been hit.

The UN Security Council on February 24 demanded a month-long ceasefire in Eastern Ghouta that would allow for aid deliveries and medical evacuations.

Since the ceasefire resolution was passed, two convoys of humanitarian assistance have entered the besieged area, but no medical evacuations have taken place.