they were focusing on the so-called "Adiyaman cell" - a group of Turks, some of whom had travelled to Syria, and who were thought also to have been behind a suicide bombing in July in the town of Suruc near the Syrian border, which killed 34 people.
The cell is also believed to have been involved in the bombing of a pro-Kurdish opposition rally in the southeastern city of Diyarbakir on the eve of Turkey's last election in June.
The possibility that a group known to the authorities carried out Saturday's attack has heaped pressure on the government, already under fire from opponents for failing to give more transparent information on its investigations into the Diyarbakir and Suruc attacks.
Details of the investigations into the Diyarbakir and Suruc bombings have nevermade quickly.
But critics say Turkey has been slow to wake up to the home-grown threat it faces from Islamic State.
Thousands of foreign fighters, including Turks, crossed the border into Syria to join the ranks of the radical group, a flow Turkey has only recently brought under control.
The Radikal newspaper said on Tuesday police had identified 21 suspected Islamic State militants, six of them women, believed to be preparing an attack in Turkey. It said 18 of them were from Adiyaman.

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