Turkish special operations police on Monday arrested 48 suspected members of the al-Qaeda terrorist group, the private television station NTV reported.
In a series of coordinated operations, 16 people were detained in Istanbul and 25 in the central Anatolian city of Konya. Other arrests were made in Izmir, Kocaeli and Mardin.
There were no initial reports on whether the suspects had been planning any operations within Turkey or abroad.
A group of Turkish religious extremists with close links to Al-Qaeda were behind a series of four suicide bomb attacks in Istanbul in Nov 2003, which left more than 60 people dead.
The suicide bombers drove small trucks laden with explosives into two synagogues on Nov 15, 2003, and five days later attacked the British consulate in Istanbul and the Istanbul headquarters of the London-based HSBC bank.