A Turkish court on Wednesday sentenced the exiled former editor-in-chief of the Cumhuriyet daily to more than 27 years in jail on espionage and terror charges for one of the reputable paper's stories.

The court found Can Dundar -- who fled to Germany in 2016 -- guilty in connection with an article about an alleged Turkish arms shipment to Islamist Syrian rebels fighting President Bashar al-Assad.

He was sentenced to 18 years and nine months for "securing confidential information for espionage" and eight years and nine months for "aiding a terrorist group" led by US-based Muslim preacher Fethullah Gulen.

The Turkish government blames the cleric for orchestrating a 2016 coup attempt against President Recep Tayyip Erdogan.

Dundar called the ruling a political "vendetta" organised against him by Erdogan.

The Turkish leader had warned Dundar that he would "pay a heavy price" when the story was first published together with an accompanying video of the alleged weapons supplies in 2015.

"This is a political decision, a vendetta which has nothing to do with law," Dundar told AFP by phone from Germany.

"Erdogan already warned me that I would pay a price. Now he is trying to have me pay a price."

Rights groups routinely accuse Turkey of undermining press freedom by arresting journalists and shutting down critical media outlets.

The US-based Committee to Protect Journalists listed Turkey as one of the top jailers after China in its annual global report last week.

It found 37 journalists were imprisoned this year -- less than half the number arrested in 2016 around the time of the coup attempt.

"What can we think of a judicial system that sentences a journalist to such a heavy sentence for simply doing his job?" the European Federation of Journalists' chief Ricardo Gutierrez asked.

Pauline Ades-Mevel of Reporters Without Borders (RSF) said Dundar's case "illustrates to the highest degree" the judicial harassment faced by journalists in Turkey.

"This is a senseless and despicable decision that confirms that President Erdogan's regime does not know how to stop in its authoritarian headlong rush," she said.

Dundar was able to flee to Germany after being released while awaiting an appeal hearing
Dundar was able to flee to Germany after being released while awaiting an appeal hearing AFP / Odd ANDERSEN

But Erdogan's media aide Fahrettin Altun tweeted that calling Dundar "a journalist -- and his sentence, a blow to free speech -- is an insult to real journalists everywhere".

Dundar's lawyers boycotted Wednesday's hearing because they did not believe they would get a fair trial.

"These are show trials," his lawyer Tora Pekin told AFP.

The Cumhuriyet daily's hard-hitting articles have often irritated Erdogan's government and the paper's reporters have routinely ended up in court.

The country's oldest daily -- which means "Republic" in Turkish -- was founded in 1924 and remains one of the few media outlets not controlled by government-allied tycoons.

Dundar was first jailed in 2015 over the paper's allegations that Turkey's MIT intelligence service was funnelling weapons to Syrian insurgents in trucks packed with boxes marked up as carrying medical supplies.

Turkey vocally opposed Assad's regime but the story appeared to reveal a covert military operation.

He was sentenced to nearly six years in May 2016 for "obtaining and disclosing classified documents related to the security of the state" but released pending an appeal.

The 59-year-old was shot at by an assailant outside Istanbul's main courthouse during that hearing.

Dundar fled to Germany later that same year and the gunman was sentenced to 10 months in jail.

The Supreme Court of Appeals reversed Dundar's conviction in 2018. The Istanbul court then began his retrial.

Turkish authorities have already requested Dundar's extradition from Germany.

"Instead of endorsing his crimes, our counterparts should extradite him to Turkey," Erdogan press aide Altun tweeted.

A court ordered the seizure of his property and froze his Turkish bank accounts in October.