A suspected senior leader of Daesh, arrested Tuesday by Istanbul police's anti-terror branch, was interrogated in northwestern Turkey's Sakarya Wednesday.
Halis Bayancuk, also known as Abu Hanzala was arrested in anti-Daesh operations in Istanbul carried out by Sakarya Chief Public Prosecutor's Office, a source confirmed.
The source, on condition of anonymity, said Bayancuk is being accused of leading Daesh supporters and sympathizers in Turkey.
The suspect was arrested earlier in 2015, among a number of detainees held across Turkey in a major nationwide anti-terror operation. Police have also detained his wife and seized digital material and documents from his home in Istanbul's Bağcılar district.
He was jailed pending trial on charges of "leading or being a member of a terrorist organization."
In a hearing in February 2016, Bayancuk rejected any link with any terrorist organization and later in March, he was released under judicial control along with dozens of other suspects.
The suspect was also arrested back in 2014 and 2011, as police raided al-Qaida cells in Istanbul. He had been suspected of being al-Qaida's alleged leader in Turkey.
Daesh is blamed for a string of attacks in Turkey, ranging from suicide bombings to gun attacks.
In January, a lone Daesh gunman stormed a popular nightclub in Istanbul, killing 39 at a New Year's celebrations. The gunman was caught a few weeks later.
Turkey is one of the main "enemies" of Daesh, which emerged in Iraq and Syria, Turkey's two neighbors.
Turkey has also been tackling an influx of foreign fighters looking to sneak into Syria and Iraq, where Daesh controls towns and a large swathe of territories.
Since Daesh's emergence, Turkey has detained over 5,000 Daesh suspects, deported over 3,290 foreign terrorist fighters from 95 countries, and refused entry to more than 38,269 individuals, in anti-terror drives.
Turkey also launched Operation Euphrates Shield last year and backed Syrian opposition groups fighting Daesh in Syria.
The operation, taking place between August 2016 and April 2017, saw the liberation of the Syrian towns of Jarablus, al-Rai, Dabiq and al-Bab from Daesh control.