Ilhan Elieyioglu, former head of Information Systems at the Telecommunications Directorate, was questioned the same day by a prosecutor in Ankara about other charges besides espionage, including "destroying the integrity of the state and irregular eavesdropping on cryptographic and ordinary phones."

Following the four-hour interrogation, Elieyioglu was sent to court for arrest.

Earlier on Thursday, a court ordered the arrest of four people and the release of seven others out of 11 recently held over alleged illegal wiretapping as part of the "parallel state" operations.

All those held were from the country`s Telecommunications Directorate.

On Wednesday, police detained 26 suspects, sending 11 of them to court for arrest.

Operations started after it was confirmed that encrypted phones belonging to senior Turkish leaders had been compromised.

Those affected include President Recep Tayyip Erdogan, PM Ahmet Davutoglu, Turkey`s Supreme Court head Hasim Kilic, General Staff chief Necdet Ozel and Deputy PMs Bulent Arinc and Ali Babacan.

Phones belonging to other senior figures such as Interior Minister Efkan Ala, Energy Minister Taner Yildiz, head of the country`s top spy agency Hakan Fidan, in addition to members of the National Security Council, were also thought to have been wiretapped.

In total, 363 incidents of illegal wiretapping of the aforementioned names have been confirmed, most of which were carried out between Dec. 17-25, 2013, when an anti-graft probe targeted a number of high-profile figures, including the sons of three former government ministers and leading Turkish businessmen.

The government has denounced the probe as a "dirty plot" constructed by the "parallel state" - a name given by authorities to an alleged group of Turkish bureaucrats and senior officials embedded in the country`s institutions, including the judiciary and the police, who have reportedly worked to undermine the Turkish state.

More about: