An Istanbul court has ordered the release of seven suspects in the trial of staff from the Cumhuriyet opposition newspaper but said other prominent defendants should be kept in jail.

The trial in Istanbul of 17 writers, cartoonists and executives from Cumhuriyet (Republic) on "terror" charges - ridiculed as absurd by supporters - began earlier this week.

The seven, including cartoonist Musa Kart, will be released under judicial supervision, meaning they have to report to the authorities regularly in the lead-up to the next hearing on September 11.

The court on Friday ruled, however, that five other employees of Cumhuriyet should remain jailed until the end of the trial.

They include the newspaper's chief editor and a prominent columnist.

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The staff are charged with supporting in their coverage three groups that Turkey considers "terror" groups - the Kurdistan Workers' Party (PKK), the ultra-left Revolutionary People's Liberation Party-Front (DHKP-C), and the organisation of Fethullah Gulen, the US-based Muslim leader accused by Turkey of ordering last year's failed coup attempt.

Those to be released were expected to walk free later from Silviri jail outside Istanbul after completing the prison formalities.

Their arrests are part of a widespread crackdown in the wake of a failed coup attempt last year, which has led to the imprisonment of more than 50,000 people.

'Long live freedom'

One of Turkey's oldest newspapers, Cumhuriyet has been fiercely critical of President Recep Tayyip Erdogan, causing anger in the halls of power with embarrassing scoops.

Since Monday, journalists from the daily have given powerful testimony, rejecting as absurd the terror charges laid against them.

Ahmet Sik, one of Turkey's most famous investigative journalists, made a defiant stand in the courtroom on Wednesday, describing what he said was the Erdogan government's past cooperation with the Gulen movement.

"This is not a statement for my defence, because I consider doing so as an insult to journalism and to the ethical values of my profession. Because journalism is not a crime," he said.

In 2011, Sik was imprisoned after writing one of the few full-scale investigations into Gulen's organisation.

"We know that what scares the tyrants most is courage," he said.

Sik could now face new charges over the statement after the complaint by prosecutors.