Turkey is investigating whether a newspaper breached terrorism laws after it published footage claiming to prove a convoy stopped last year was carrying arms to Syrian rebels.
The trucks, allegedly owned by Turkish intelligence, were searched in January 2014 near the border.
The pro-opposition Cumhuriyet daily said they held weapons stashed below boxes of medicine.
Turkey has said the vehicles were on a humanitarian mission.
The government has claimed that the raid on the trucks was carried out on the orders of supporters of Fethullah Gulen, the US-based cleric who Ankara accuses of running a parallel state.
The prosecutors who ordered the search and the military officers who carried it out are also under investigation.
Cumhuriyet said their footage had been taken by local security officials.
The vehicles carried mortar shells, grenade launchers and tens of thousands of rounds of ammunition, it alleged.
The leader of Turkey's main opposition party, Kemal Kilicdaroglu, called the information "extraordinary".
"Those who illegally sent arms to a Muslim country have blood on their hands," he told the AFP news agency.
Turkey has denied arming Islamist fighters in Syria.
The news comes as Syrian rebels continue to make advances in Idlib province, which borders Turkey.
Their advance is thought to have been aided by an alliance between Turkey, Qatar and Saudi Arabia, all of whom want Syrian President Bashar al-Assad ousted.