Turkish authorities detained two former policemen following their extradition from Romania on suspicion of bugging President Recep Tayyip Erdogan, state media said Sunday.

Sedat Zavar, a former police chief, and Ilker Usta, were detained at Istanbul airport late Saturday after their arrival on a flight from Bucharest, the Anatolia news agency reported.

They face up to 36 years in jail on charges of "forming a crime syndicate", "violating privacy" and "illegally obtaining personal information," Anatolia said.

They are expected to appear in court on May 4.

The detentions are a part of an intensifying crackdown against followers of US-based preacher Fethullah Gulen, accused by Erdogan of setting up a "parallel state" seeking to oust him from power and concocting a corruption scandal that rocked the government in late 2013.

The authorities accuse police of bugging Erdogan and other top officials at the behest of Gulen, whose extradition is being sought by Turkey.

Since becoming president in August 2014, Erdogan has intensified his offensive against Gulen followers and the authorities have conducted raids against dozens of police officers accused in the spying case.