Jihadists from the Islamic State group have seized parts of a military base in Syria's Raqa province in fierce fighting that left dozens dead, a monitor said yesterday.

The Syrian Observatory for Human Rights said the extremist group was engaged in heavy fighting with troops at Brigade 93 in Raqa, where IS already controls the regional capital and significant amounts of territory.

The monitor said at least 27 regime forces had been killed, along with 11 jihadists, including three who launched the assault by blowing themselves up at the entrance to the base and around it on Wednesday night.

The Observatory said IS fighters "were in control of large parts of the base".

Many regime troops had withdrawn to Brigade 93 last month, after IS seized the Division 17 base in fighting that left at least 85 soldiers dead, according to the Observatory.

That assault left nearly all of Raqa province under IS control, except Brigade 93 and Tabaqa military airport, which were still held by the army.

The two-day assault on Division 17 saw more than 50 troops summarily executed, including some who were beheaded, with jihadists later putting their severed heads on display.