People in need of medical treatment have been evacuated from the besieged rebel-held Eastern Ghouta area on the outskirts of Syria's capital, Damascus.

Twenty-five patients and their families are believed to have left via a government checkpoint on Wednesday.

Another 31 were evacuated on Tuesday as part of an agreement between a rebel group and the government's ally Russia.

More than 1,100 civilians have been killed since pro-government forces stepped up an offensive a month ago.

In recent days, dramatic advances by soldiers and militiamen have displaced thousands of civilians and cut the enclave into three pockets.

UN Secretary General António Guterres says the estimated 390,000 people trapped there are "living in a hell on earth", forced to shelter from the bombardment in overcrowded basements where access to food, water and sanitation is limited.

The Syrian American Medical Society (SAMS), which supports a number of medical facilities in the Eastern Ghouta, said on Tuesday that at least 1,034 critically ill and wounded people were in need of medical evacuation. They included 77 "priority cases".

As a result of the agreement between Russia and the rebel group Jaysh al-Islam, which controls the northern pocket around the major town of Douma, at least 55 patients on the list are reported to have left during pauses in the fighting.