At least 39 Syrian military personnel were killed during raging battles with the Islamic State (IS) group at a besieged northern airbase, a monitor group reported Wednesday.

A total of 39 army men, including 31 officers, have so far been killed during intense battles that have been raging since Sunday at the Koerse airbase in the countryside of the northern province of Aleppo, according to the Syrian Observatory for Human Rights.

The UK-based watchdog group said 33 IS militants were also killed during the days-long battles at Koerse.

The airbase has for long been besieged by the IS militants, who also repeatedly attempted to storm this crucial facility, but so far failed.

Koerse, which has been besieged by the rebels since two years ago, is the biggest airbase in Syria, stretching on a five square kilometers of land and including the Aviation Faculty, one of the biggest in the Middle East.

The airbase, which is run by around 2,000 army men, is deemed as the regime bastion in Aleppo. Several rebel and jihadi groups staged several attempts to storm the sprawling faculty, but couldn't succeed due to its heavy fortification.

The base is used by the Syrian warplane to strike the rebel-held areas and the positions of the IS in Aleppo, which made it a target to the rebels to eliminate.

The Syrian military has lost several key airbases to the rebels in the recent years of the crisis, and losing Koerse would be a severe blow to the Syrian army.