IS fighters launched an early-morning attack on Saturday and captured several buildings in Deir el-Zour, including the Assad Hospital. The militants also cut off a supply route between the Syrian army and the airport.

The government troops then fought back and recaptured the hospital, although the fighting still continued in the area.

The UK-based Syrian Observatory for Human Rights said Saturday that IS killed at least 35 members of the Syrian army and detained some medical staff from the hospital. Some 24 IS militants were also killed during the fighting in and around the hospital.

IS controls most parts of the Deir el-Zour province. Since March last year, it has laid siege to the government-held areas in the city of the same name, which borders Iraq. The province links the group's de facto capital Raqqa in Syria and IS-held territories in Iraq.

According to Syrian opposition activist Omar Abu Leila, who now lives in Europe, IS militants launched offensives from several fronts at the same time, which make them different from its previous offensives.

Syrian and Russian air force regularly strike IS targets in Deir el-Zour and also air drops aid for the besieged citizens.

shs/jm (Reuters, AP)