Turkey's ruling party on Friday ordered a purge from its ranks of supporters of US-based Islamic preacher Fethullah Gulen, accused of plotting last month's failed coup.

The "urgent clean-up in the party organisation" was aimed at expelling those linked with the Fethullah Terrorist Organisation, as Ankara calls the movement blamed for the July 15 attempted putsch, state-run Anadolu news agency reported.

It comes as Turkey announced a visit later this month from US Secretary of State John Kerry, which would be the first by a western diplomat since the failed effort to unseat President Recep Tayyip Erdogan's government.

Turkey's hardline response to the coup has escalated tensions with Europe, while the United States, where Gulen has been in self-imposed exile since 1999, has not yet confirmed the key visit by its top diplomat.

Ankara has accused Erdogan's arch-foe Gulen of running a "parallel state" and on Thursday issued a warrant for his arrest for "ordering the July 15 coup" -- which the reclusive cleric vehemently denies.

The Muslim cleric has denounced the arrest warrant as meaningless, and his lawyer told reporters in Washington Friday that Turkey did not have any evidence linking Gulen to the failed coup.

"We haven't seen any evidence, direct or indirect... a scintilla of evidence, electronic or otherwise, implicating Mr Gulen," said attorney Reid Weingarten.

Turkey has frequently called on the United States to extradite Gulen, sending documents to Washington as evidence of his alleged involvement in the putsch attempt.

But Weingarten accused Erdogan of betting on "power and politics" to make Washington grant the extradition.

"The bottom line is that the conspiracy theories and the threats of Mr Erdogan are not strong enough to overwhelm the American legal system. And for these reasons, we believe that Mr Gulen should not and will not be extradited," Weingarten said.

- Links to Kazakhstan -

Turkish authorities have implemented a relentless crackdown in the wake of the coup.

Over 60,000 people within the military, judiciary, civil service and education have been dismissed, detained or are currently under investigation for suspected links to the Gulen movement.

A German national has also been caught up in the purge, Berlin confirmed Friday.

A woman was arrested several days ago after books were found at her home suggesting she had links with the Gulen movement or was a member of it.

The German embassy in Ankara has been trying to contact the woman for several days, without success, said the Sueddeutsche Zeitung newspaper, which initially reported the arrest.

Turkey is also pressing Kazakhstan over its schools linked to Gulen, with Erdogan expressing the hope on Friday that the Central Asian country would take steps to close them.

"They (Gulenists) have 33 schools in Kazakhstan. We have delivered them the list," Erdogan told reporters in Ankara with Kazakhstan's President Nursultan Nazarbayev, the first foreign head of state to visit Turkey after the failed coup.

The Kazakh leader said 90,000 students were registered at those schools.

"If there are any among them linked with terrorism... we will respond to Turkey's demand," he said.

Ankara's crackdown on the Gulen movement has also targeted journalists accused of links to the preacher.

Twelve out of 14 journalist suspects from the Zaman daily were remanded in custody, Anadolu reported on Friday, less than a week after six others were arrested.

Mumtazer Turkone, former columnist of the newspaper, was one of the journalists arrested by an Istanbul court, on charges of "serving FETO's purposes," it added.

Meanwhile, Foreign Minister Mevlut Cavusoglu escalated a war of words with Austria on Friday, calling it the "capital of radical racism" after Vienna urged an end to Ankara's EU membership talks.

"Racism is an enemy of human rights and humanitarian values and the Austrian chancellor should first look at his own country," he told TGRT news channel.

"Austria is the capital of radical racism," he added.

Reacting on Twitter soon after Cavusoglu made those comments, Austrian Foreign Minister Sebastian Kurz urged his counterpart to "exercise restraint".

"Turkey needs to moderate its choice of words and actions," he said.

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