Turkey was on Saturday holding 17 journalists on charges of "terror group" membership as President Recep Tayyip Erdogan told Western critics to "mind your own business" over a relentless crackdown following a failed coup.

But in a goodwill gesture two weeks after the July 15 coup bid, Erdogan also announced he was withdrawing thousands of lawsuits against individuals accused of insulting him.

Turkey has detained more than 18,000 people over the attempted putsch which has been blamed on the US-based preacher Fethullah Gulen -- a charge he denies -- with the crackdown sparking warnings from Brussels that Ankara's EU membership bid may be in danger.

Seventeen journalists remanded in custody by an Istanbul court over links to Gulen woke up in jails across the city on Saturday as international concern grows over the targeting of reporters in the wake of the thwarted putsch.

Twenty-one journalists had appeared before a judge in hearings lasting until midnight on Friday. Four were then freed but the rest were placed under pre-trial arrest, charged with "membership of a terror group", the state-run Anadolu news agency said.

Those held include the veteran journalist Nazli Ilicak as well as the former correspondent for the pro-Gulen Zaman daily Hanim Busra Erdal.

Among those freed was prominent commentator Bulent Mumay who was given a rapturous welcome by supporters.

"I could never have imagined being accused of such a thing. It was madness. It's not right to arrest journalists -- this country should not make the same mistakes again," he said, quoted by the Dogan news agency.

Foreign Minister Mevlut Cavusoglu defended the detention of reporters, saying it was necessary to distinguish between coup plotters and those "who are engaged in real journalism".

Erdogan also announced that as a gesture of goodwill after the coup he was dropping hundreds of lawsuits against individuals accused of "disrespectful" insults against him.

Earlier this year, officials had said more than 2,000 people were being prosecuted on charges of insulting the president, from a provincial schoolboy to a former Miss Turkey.

- 'Mind your own business!' -

Thousands of those detained after the coup have now been released, with an Istanbul court freeing 758 soldiers late on Friday, adding to another 3,500 former suspects already set free.

Among those released were 62 students from Istanbul's military academy -- many said to be in their teens -- who left Maltepe jail to an emotional reunion with relatives, Dogan news agency said.

But with concern growing about the sheer numbers rounded-up, EU enlargement commissioner Johannes Hahn said he needed to see "black-and-white facts about how these people are treated".

"And if there is even the slightest doubt that the (treatment) is improper, then the consequences will be inevitable," he told German daily Sueddeutsche Zeitung.

In a speech at his presidential palace late on Friday remembering those killed during the failed coup, Erdogan angrily denounced the criticism and accused the West of deserting Turkey in its hour of need.

"Some people give us advice. They say they are worried. Mind your own business! Look at your own deeds," Erdogan said.

One of the very few EU officials of any rank to visit Turkey in the wake of the coup was Alan Duncan, a junior minister within Britain's foreign office.

Erdogan on Saturday met with Foreign Minister Mohammed Abdulrahman al-Thani of Qatar, one of Turkey's closest allies.

Tens of thousands of Erdogan supporters are due to rally in the German city of Cologne on Sunday with the German authorities on edge to prevent any clashes.

- 'Taking the plotters' side' -

Turkey implemented a shake-up of the military on Thursday after nearly half of its 358 generals were sacked for complicity in the coup.

A senior official said on Saturday that Turkey had intercepted encrypted messages sent by followers of Gulen on the app ByLock well before the coup attempt, giving Ankara names of tens of thousands within the preacher's network.

Erdogan had earlier also lashed out at a top US general who had expressed concerns about military relations after the putsch, accusing him of "taking the side of the plotters".

Quoted by US media, US Central Command chief General Joseph Votel said on Thursday that the coup bid and subsequent round-up of dozens of generals could affect American cooperation with Turkey. Votel swiftly denied any link to the coup however.