ISTANBUL (AFP) - Turkish police on Monday raided four major courts in Istanbul in search of 190 suspects wanted over last month's attempted coup, state media said.

In total, 136 of the wanted prosecutors and other judicial staff working at the courts have been detained, the official Anadolu news agency said.

They are suspected of links to US-based Islamic preacher Fethullah Gulen who Ankara blames for the putsch against President Recep Tayyip Erdogan on the night of July 15.

According to official figures, more than 35,000 people have been detained so far in the post-coup crackdown against alleged Gulen supporters, although almost 11,600 have since been released.

Erdogan has said the purge is needed to wipe out what he calls the "virus" of Gulen from Turkish institutions. But critics have expressed alarm that its sheer scope has turned it into a witch hunt.

In a separate development, the former chief prosecutor for the eastern region of Erzurum was detained late Sunday while trying to cross into Syria.

Ekrem Beyaztas was caught by border guards just south of the Turkish town of Kilis, a Turkish official said, asking not to be named. There was no indication over why he had been heading to Syria.