Jihadists from the Islamic State of Iraq and Greater Syria (ISIS or ISIL) have seized parts of a military base in Syria's Raqa province in an assault that left dozens dead, a rights group said

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

The Observatory said that at least 27 Syrian troops had been killed, along with 11 jihadists. Three militants launched the assault by blowing themselves up at the entrance to the base on Wednesday night.

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

ISIS jihadists have recently seized a string of towns in northern Iraq.

The militant group, which began taking part in Syria's war in spring 2013, has since imposed near-total control in Raqa province and Deir Ezzor on the Iraq border.

Most troops had withdrawn to Brigade 93 last month, after ISIS seized the Division 17 base in fighting that left at least 85 soldiers dead, according to the Observatory.

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

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

 (AFP)