Twenty-one journalists are appearing in court in Istanbul after being detained as part of a sweeping crackdown following Turkey's failed military coup.

Television footage showed police leading the journalists to the courthouse. They are among 42 for whom detention orders were issued on Monday, while authorities are searching for those still at large, the state-run Anadolu agency said.

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Turkey declared a state of emergency after the failed coup on July 15 that caused 290 deaths. The clampdown is targeting those suspected of ties to US-based Muslim cleric Fethullah Gulen, whom the government accuses of masterminding the plot. He has denied any involvement.

Nearly 16,000 people have been detained so far over alleged links to the uprising. Tens of thousands of civil servants have been dismissed for alleged ties to Mr Gulen, according to Anadolu, from sectors including the judiciary, education, health care, local municipalities and ministries.

"If we hadn't removed the people this coup attempt would have been successful," foreign minister Mevlut Cavusoglu told reporters in Ankara. "Every state has to take its own measures to ensure that it does not come face to face with such a threat again. No state would allow such a threat to remain in its midst."

Authorities have issued warrants for the detention of 89 journalists, and dozens of media organisations, mostly linked to Mr Gulen, were ordered to close on Wednesday night.

"These journalists worked in media organisations that belonged to this terror organisation," Mr Cavusoglu said.

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"They were not only engaged in journalistic activity, they were engaged in activities that included the fabrication of evidence that served (the Gulen movement)," he said. "We need to make a distinction between those who co-operate with those who carried out the coup, those who supported it and the real journalists."

He added: "If they are engaged in a crime, they cannot be untouchable or exempt from prosecution. That's what we believe, but we will continue to defend freedom of press and freedom of expression till the end."

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Investigations into people's involvement with the Gulen movement, "the financial support they provided and their participation in other activities are continuing", the minister said.

"All politicians, including the president, were on a death list. We are forced to take these measures," he said.

Meanwhile, the Ministry of European Union Affairs suspended 16 staff and dismissed six others as part of the investigation into the Gulen movement, while the public prosecutor's office in the Aegean coastal town of Izmir issued orders for 203 police personnel to be apprehended, Anadolu said.

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Teams from the Izmir Police Department Counterterrorism Bureau conducted simultaneous operations around the city and apprehended several suspects, the agency reported.