Deir al-Zor : The Islamic State militant group (ISIS) attacked a hospital in Deir al-Zor on Saturday and seized territory on the edge of the besieged eastern Syrian city still partly controlled by the government, the militant group said.

ISIS's Amaq news agency said its fighters stormed the Assad Hospital and also took control of a check point, a fire station and university accommodation in the city close to Syria's eastern border with Iraq.

ISIS controls most of Deir al-Zor province and has laid siege since March last year to the remaining government-held areas in the city of the same name.

Deir al-Zor province links ISIS's de facto capital in the Syrian city of Raqqa with territory controlled by the militant group in neighboring Iraq. The Syrian Observatory for Human Rights said there were reports ISIS had detained medical staff and taken some government soldiers prisoner in Deir al-Zor.

It said there were ongoing fierce clashes between government forces and ISIS in the area after the militants attacked the southwestern edge of the city at dawn.

The fighting killed at least 20 members of the Syrian government forces and at least six ISIS fighters, the Observatory said.

Amaq news agency also said the Islamist militants had taken territory near to the state-held military airport. Russia's RIA state news agency on Saturday reported a source within the airbase as saying an Islamic State attack had been repelled.

The Syrian government and its Russian allies make regular aid drops into the encircled city, and there are frequent air strikes on ISIS targets in and around Deir al-Zor.