A Turkish court on Wednesday sentenced a prominent opposition lawmaker to 25 years in prison on espionage charges, prompting an outcry from his party.

Enis Berberoglu, a 61-year-old former journalist and a member of the pro-secular Republican People's Party, or CHP, was convicted of revealing state secrets, Turkey's official Anadolu news agency said.

The case stems from a May 2015 report in the Cumhuriyet newspaper suggesting Turkey's intelligence service had smuggled weapons to Islamist rebels in Syria a year earlier — which the government denied. Berberoglu was accused of giving journalists images used in the report.

He faced a life sentence but the court reduced it for "good behavior." Berberoglu said justice had been "slaughtered" as he was led out of the court following the verdict.

"I know you won't forget me and I won't forget you," he told reporters.

His lawyer said the verdict would be appealed.

Can Dundar, Cumhuriyet's then editor-in-chief who is now abroad, and its Ankara representative, Erdem Gul, are also on trial on similar charges. Separately, the three are being tried for "aiding a terror organization without being members," referring to the network of U.S.-based cleric Fethullah Gulen who Turkey claims orchestrated last summer's bloody coup. Gulen has denied the claims.

CHP lawmakers left parliament to protest the verdict Wednesday.

"Can there be a country with no justice, can there be a state with no justice?" party leader Kemal Kilicdaroglu asked. "They are putting dynamite to the foundations of the state."

He said he would begin a protest in Ankara on Thursday and also organize a march to the Istanbul prison where Berberoglu has been incarcerated.

Earlier this year, the Istanbul court said the leaked images — also blamed on Gulen — aimed to manipulate international opinion and "have Turkey put on trial as a country supporting terror," Anadolu said.

Cumhuriyet said the images were from 2014 and showed local authorities searching Syria-bound trucks carrying mortar rounds and getting into a standoff with Turkish intelligence officials. Turkish leaders denied supporting Islamic rebels and said the trucks contained aid to Turkmens in Syria.

Last year Berberoglu told Turkish media that Cumhuriyet's story was accurate but would not confirm he was the source of the images.

CHP leader Kilicdaroglu tweeted, "In this country, the punishment for covering the news of a truck filled with weapons heading to terror groups is 25 years in prison but illegal arm shipments are allowed!"

Berberoglu is the first CHP legislator to be imprisoned since a constitutional amendment stripped parliamentary immunities last year. A dozen pro-Kurdish lawmakers are already in prison for allegedly supporting terror and more than 50,000 people have been arrested for purported links to Gulen.

Separately, Cumhuriyet's online editor Oguz Guven was released from prison pending trial after his arrest last month for allegedly spreading "terror propaganda" for Gulen.