By Ayla Jean Yackley
ISTANBUL (Reuters) - Several thousand people protested on Friday over the arrest of two prominent journalists on charges of espionage and terrorist propaganda, a case that has revived long-standing criticism of Turkey's record on press freedom under President Tayyip Erdogan.
A court on Thursday ordered the arrest of Can Dundar, editor-in-chief of Cumhuriyet newspaper, and senior editor Erdem Gul over the publication of footage purporting to show the state intelligence agency helping send weapons to Syria.
The United States said it was "very concerned," and opposition politicians fiercely criticized the move.
"Journalism is being put on trial with these arrests and the Turkish press is being intimidated," Utku Cakirozer, a deputy from the main opposition People's Republican Party (CHP) and Cumhuriyet's former top editor, told Reuters.
Some 2,000 people gathered in Istanbul, with some chanting "Murderer Erdogan" and accusing the ruling AK Party he founded of collaborating with Islamic State. Some demonstrators held up Friday's edition of Cumhuriyet, which carried the headline "Black day for the press". Cumhuriyet is a secular, left-wing newspaper that is often critical of the government.
"All opposition press organizations that are abiding by the ethics of journalism and trying to do their journalism are under threat and under attack," Figen Yuksekdag, co-chairwoman of the pro-Kurdish Peoples' Democratic Party, said at the protest.
"This dark operation aimed at covering the crimes that those trucks carried and the crimes which are continuing to be committed will not be successful," she added.
The video footage, released in May, purported to show Turkish police opening crates of weapons and ammunition bound for Syria on the back of trucks said to belong to the MIT National Intelligence Organisation.
Publication of the story at the time prompted Erdogan to vow revenge, saying those behind it endangered security and would "pay a heavy price".
He subsequently filed a criminal complaint against Dundar and Gul.
Dundar rejected the charges in his defense on Thursday.
"It may be the duty of someone working for the state to rescue it from a difficult situation, but a journalist is not a civil servant," he said, according to a transcript printed by Cumhuriyet, one of Turkey's oldest dailies.
In the capital Ankara, about 1,000 people including MPs gathered for a protest over the arrests and police fired pepper gas at the crowd as they sought to march. "Shoulder-to-shoulder against fascism," the crowd chanted.
"We are very concerned by the arrests of Can Dundar and Erdem Gul and what appears to be yet another media outlet under pressure," the U.S. Embassy said on Twitter.
"We hope the Turkish courts and authorities will uphold the fundamental principle of media freedom enshrined in the Turkish Constitution."
There was also criticism from the Council of Europe, with its human rights commissioner Nils Muiznieks describing the arrests in a tweet as "another blow to media freedom in Turkey".
European diplomats are measured in their criticism of media freedom in Turkey and Erdogan's increasingly authoritarian rule, recognizing the West needs Ankara's help on the migrant crisis and as an ally in the U.S.-led coalition against Islamic State.
Europe is hoping to finalize a deal with Ankara - a NATO member and a candidate for EU membership - on the refugee crisis at a summit this weekend.
(Additional reporting by Gulsen Solaker in Ankara; Writing by Daren Butler; Editing by David Dolan and Ralph Boulton)