By Daren Butler
ISTANBUL (Reuters) - Turkish police raided offices at three Istanbul courthouses on Monday after detention warrants were issued for 173 judicial personnel as part of an investigation into last month's failed coup attempt, the private Dogan news agency reported on Monday.
More than 35,000 people have been detained, of whom 17,000 have been placed under formal arrest, and tens of thousands more suspended since the July 15 putsch, which authorities blame on U.S.-based Muslim cleric Fethullah Gulen and his followers.
President Tayyip Erdogan demands the United States extradite Gulen, and the purge is straining relations with Western allies who Turkish officials say appear more concerned by the crackdown than the failed coup that killed 240 people.
Police were searching the offices of personnel facing detention at the main Istanbul Palace of Justice in the Caglayan district and two other court houses on the European side of the city, Dogan said.
The agency said police took some of those detained away from Caglayan for questioning at a police station. The homes of those being detained were also being searched, state-run Anadolu Agency reported.
In the crackdown since the abortive coup, more than 76,000 civil servants, judges and security force members have been suspended and nearly 5,000 dismissed, Prime Minister Binali Yildirim said on Saturday.
Western officials are concerned the purge will impact stability in the NATO member and a key partner in their war on Islamic State in neighboring Iraq and Syria. Turkish officials say they are confronting an internal threat.
Amid the rising tension with the West, Turkey has sought to normalize relations with Russia, sparking fears that Erdogan and Russian President Vladimir Putin might use their rapprochement to exert pressure on Washington and the European Union and stir tensions within NATO.
In keeping with Erdogan's tough line on Gulen, Yildirim told local reporters there would be no compromise apart from "this chief terrorist coming to Turkey and being prosecuted," according to Anadolu agency.
Turkish officials say they have handed over documents to U.S. officials concerning Gulen. Washington has been cautious, saying it needs clear evidence and a U.S. Department of Justice team is expected in Turkey later this month.
Gulen, who has lived in self-imposed exile in Pennsylvania since 1999, denies any role and condemned the coup bid. But Turkish officials say his network of followers inside state institutions masterminded the putsch when rogue soldiers commandeered tanks, warplanes and helicopters.
In another arrest, a prosecutor in eastern Turkey, who had been suspended under the coup investigation, was detained as he tried to cross the border into Syria on Sunday night, a Turkish government official said.
He said Ekrem Beyaztas, chief prosecutor in Erzurum province, was detained by border guards in Kilis province. There was a warrant for his detention.
"Our initial assessment is that he was trying to reach PYD-controlled parts of northern Syria in an attempt to seek protection," the official said.
Ankara regards the PYD, the main Syrian Kurdish party, as a terrorist group due to its links to the militant Kurdistan Workers Party (PKK) which has fought a three-decades-old insurgency against the Turkish state.
"In recent weeks, runaway coup plotters have been trying to leave Turkey via routes traditionally used by the PKK to smuggle militants and weapons in and out of the country," he said.
Separately, a senior intelligence officer said operatives linked to Gulen have had an active relationship with PKK militants.
"In recent weeks, runaway operatives that successfully reached Iraq have been accompanied by PKK elements on the ground," the officer said.
The officer said some Gulen-linked operatives have been offered safe passage to Europe in return for information about ongoing operations and working methods of the MIT intelligence service and the military.
Two fugitive staff colonels accused of involvement in the coup were detained in the central Turkish city of Konya along with one person helping to hide them, Anadolu said. They were flown to Istanbul for questioning.
It said one of the officers was accused of commanding soldiers to open fire on protesters on Istanbul's Bosphorus bridge in Istanbul and the other of ordering a raid on the state broadcaster TRT on the night of the coup.
Turkey is also seeking more than 30 diplomats who fled to other countries after they were recalled to Ankara as part of the post-coup investigation. Several military attaches are also on the run after refusing to return home.
(Editing by David Dolan and Patrick Markey)