ISTANBUL — A long-awaited trial of two Turkish journalists facing potential life sentences on espionage charges began Friday, but was quickly closed to the public and news media, prompting outrage and concerns over whether the proceedings could be free and fair. A subsequent postponement, until April 1, did little to stanch the criticism.

The espionage charges are based on reporting by the journalists on weapons shipments by the country’s spy agency to Syrian rebels opposed to the government of President Bashar al-Assad. Both the charges, which press organizations have denounced as baseless, and the decision to move the trial behind closed doors were criticized by Turkish journalists, anti-government activists and foreign governments. They see the closing of the trial as a vivid demonstration of a tilt toward authoritarian rule by the government of Turkey’s president, Recep Tayyip Erdogan.

The government said it was closing the proceedings to protect state secrets, a claim that was dismissed by the hundreds of journalists, politicians, diplomats and activists packed into the courtroom for what they believed would be a public trial. When told that they would have to leave, they erupted in anti-government chants.

“You are all dogs of Tayyip, shame on you!” one woman shouted, referring to Mr. Erdogan, who personally filed the criminal complaint against the journalists and was accepted on Friday by the judge as a co-plaintiff in the case.