A private security employee stands guard at the entrance of daily newspaper Cumhuriyet's offices, in Istanbul January 14, 2015. REUTERS/Murad Sezer

ISTANBUL (Reuters) - Turkish newspaper Cumhuriyet, whose top two journalists were arrested last week on charges of espionage and terrorist propaganda, is facing an investigation into its tax accounts, its chief executive said.

A court last Thursday ordered the arrest of Can Dundar, the paper's editor-in-chief, and senior editor Erdem Gul over the publication of footage purporting to show the state intelligence agency helping to send weapons to Syria.

The case against the journalists has revived long-standing criticism of Turkey's record on press freedom under President Tayyip Erdogan with the United States saying it was "very concerned" about the arrests.

"They informed (us) that they will once again inspect Cumhuriyet newspaper's 2010 accounts, 2-1/2 years after fully inspecting them before," the newspaper's chief executive, Akin Atalay, wrote on Twitter on Monday.

The tweet was accompanied by a photocopy of an apparent corporation tax inspection report dating from mid-2013 regarding the company's 2010 accounts. Officials were not available to comment.

The video footage at the heart of the court case, released in May, purported to show Turkish police in 2014 opening crates of weapons and ammunition bound for Syria on the back of trucks said to belong to Turkey's MIT National Intelligence Organisation.

Chief Prosecutor Hadi Salihoglu said the police search was carried out by members of the "Gulenist terrorist organization' and that the images featured in Cumhuriyet's story were put out with the organization's goal of getting Turkey prosecuted in international courts.

Exiled preacher Fethullah Gulen, a friend turned enemy of Erdogan, is facing charges in Turkey including 'forming and leading an armed organization'.

At the time of publication, Erdogan vowed revenge, saying those behind the story had endangered Turkey's security and would "pay a heavy price".

'HONOR OF A COUNTRY'

The head of the France-based group Reporters Without Borders, which promotes press freedom, is visiting Istanbul this week to express solidarity with Dundar and Gul.

"News and information should be the honor of a country," the group's secretary-general Christophe Deloire told Reuters.

"Turkish authorities are fighting the wrong enemy," he said by phone. "We appeal to the government to restore all conditions of pluralism starting with the freedom of journalists."

The Istanbul Chief Prosecutor's office on Friday made a statement saying the investigation of Dundar and Gul had "nothing to do" with press freedom and that the stories were published "to reveal state secrets".

But Deloire said writing about security matters was part of a journalist's job.

"Dundar and Gul did their jobs and their revelations were very crucial."

(Reporting by Humeyra Pamuk and Daren Butler; Editing by Nick Macfie and Raissa Kasolowsky)