The trial of two prominent Turkish journalists, charged with revealing state secrets, has been adjourned until 1 April.
Can Dundar and Erdem Gul, from the newspaper Cumhuriyet, were arrested in November over a report alleging that the Turkish government had tried to ship arms to Islamists in Syria.
They deny the charges but face possible life sentences if found guilty.
Their supporters say the case is a major test of press freedom in Turkey.
The Turkish government has come under increasing international criticism over its treatment of journalists.
Earlier this month, Turkish police raided the offices of the country's biggest newspaper, Zaman, hours after a court ruling placed it under state control.
Over 100 reporters and observers attended the opening session of the trial on Friday morning.
Prosecutors then asked the judge for a closed hearing, a request which the judge approved, after a brief adjournment.
A Human Rights Watch observer present in the court called the decision "a travesty of justice".
The adjournment came after more than a dozen opposition MPs refused to leave the courtroom. The judges filed a complaint against them for attempting to influence the trial.
Can Dundar, Cumhuriyet's editor-in-chief, and Erdem Gul, Ankara bureau chief, were arrested last November.
President Recep Tayyip Erdogan personally filed a criminal complaint against them.
They were held in pre-trial detention but were released in February after the Constitutional Court ruled their rights to liberty and free expression had been violated.
In a statement given just before the trial, Mr Dundar said the government was trying to intimidate Turkey's journalists.
"There is an effort to arrest an entire profession and the public - what foreigners call a 'chilling effect'," he said.
"What is trying to be created is a mechanism of self-censorship and an increasing empire of fear."
Freedom of the press in Turkey
- Turkey ranks 149th amongst the 180 countries in the Reporters Without Borders' World Press Freedom Index 2015
- Media organisations in Turkey say that more than 30 journalists are currently behind bars
- Most are of Kurdish origin
- The government argues journalism in Turkey is among the most free in the world
Campaigners say the case is politically motivated and part of a growing crackdown on media critical of President Erdogan.
On Thursday, dozens of prominent writers published an open letter to Prime Minister Ahmet Davutoglu, urging the government to drop the charges against the Cumhuriyet journalists.
"We believe that Can Dundar and Erdem Gul are facing life in prison simply for carrying out their legitimate work as journalists," they said.
The letter also voiced concern over the "increasing climate of fear and censorship and the stifling of critical voices in Turkey".
Zaman newspaper is closely linked to the Hizmet movement of influential US-based cleric Fethullah Gulen.
The government says Hizmet is a "terrorist" group aiming to overthrow President Erdogan.
Mr Gulen was once an ally of Mr Erdogan but is now seen by the Turkish President as a threat to his authority.