ISTANBUL - Suicide bombers blew themselves up in the Turkish city of Gaziantep near the Syrian border on Sunday, causing an unknown number of casualties, after police raided their sleeper cell, state media reported.

The bombers detonated their explosives when they saw they were likely to be captured during an operation by Turkish security forces in the southeastern city, Anadolu news agency reported. 

Media reports spoke of casualties without providing precise numbers.

Witnesses told the private NTV television they heard the sounds of gunfire and clashes in the area, mostly populated by university students.

Many ambulances were dispatched to the scene, Anadolu reported. 

It was not immediately clear which group the sleeper cell raided by Turkish security forces belonged to. 

Turkey is reeling from a string of attacks blamed on Islamic State jihadists and Kurdish militants.

Fifty-seven people, 34 of them children, were killed in August in a suicide attack carried out by a bomber linked to IS jihadists at a Kurdish wedding in Gaziantep. 

The latest attack comes shortly after Turkey-backed opposition fighters captured the northern Syrian town of Dabiq from the IS jihadist group. (AFP)