ISIL terrorists overran the headquarters of Kurdish forces defending the battleground Syrian border town of Kobani on Friday, a monitoring group said.

ISIL terrorists overran the headquarters of Kurdish forces defending the battleground Syrian border town of Kobani on Friday, a monitoring group said.

"The 'jihadists' have taken control of the headquarters building," used by the Kurdish military and civilian authorities, the UK-based Syrian opposing Observatory for Human Rights said.

Fierce fighting had raged for the complex throughout the morning after ISIL militants captured part of it used by the Kurds' asayesh internal security force on Thursday.

"ISIL now controls 40 percent of the town," after entering eastern districts on Monday and attacking from the west and the south, said the Observatory.

"The capture of the headquarters will allow the 'jihadists' to advance on the border post with Turkey to the north of the town," the Observatory told AFP.

"If they achieve that, they will have the Kurdish forces inside Kobani completely surrounded," he added.