Two prominent Turkish journalists have been arrested on charges of assisting terrorists, CNN Turk said, after they published footage that purported to show the state intelligence agency helping send weapons to Syria.

A Turkish court ordered the arrest of the editor-in-chief of Cumhuriyet, Can Dundar, and the newspaper's Ankara correspondent, Erdem Gul, the television channel said on Thursday.

Turkish media reports said that the two faced a number of charges including membership of an armed terrorist organisation and the publishing of material in violation of state security following the release of the footage in May.

Reuters was not immediately able to verify the reports.

The video, purporting to show Turkish police opening crates of weapons and ammunition bound for Syria on the back of state security agency trucks, prompted President Tayyip Erdogan to vow revenge, saying he would not forgive such reporting.

European diplomats are measured in their criticism of media freedom in Turkey and Erdogan's increasingly authoritarian rule, recognising the West needs Ankara's help on the migrant crisis and as an ally in the US-led coalition against Islamic State.

Europe is hoping to finalise a deal with Ankara - a NATO member and a candidate for EU membership - on the refugee crisis at a summit this weekend.