State-run television TRT reports that a Syrian plane intercepted by Turkish jets was carrying military communications equipment.
Turkish officials have yet to specify what was aboard the Syrian Air A320 from Moscow that was forced to land in Ankara on Wednesday.
Turkey's Prime Minister Recep Tayyip Erdogan said the plane was carrying military equipment and ammunition destined for the Syrian military.
He told reporters in Ankara on Thursday that Turkey was still examining the equipment and that "the necessary will follow."
Turkish Foreign Minister Ahmet Davutoglu said the cargo contained "elements ... that are not legitimate in civilian flights."
Russia's Itar-TASS news agency quoted an official at the Russian embassy in Ankara saying that the cargo "was not of Russian origin."
The plane's 37 passengers and crew were allowed to continue to Damascus after several hours without the cargo.
The TRT report came as the Russian Foreign Ministry said on Thursday that Russia was demanding an explanation from Turkish authorities after Ankara detained a the civilian airplane en route from Moscow to Damascus with Russian citizens on board.
The ministry said that Turkish authorities refused to grant Russian diplomatic staff access to 17 Russian citizens on board during the eight hours that the flight was held up because of suspicions the aircraft was carrying military equipment.
"The Russian side is insisting on an explanation of the reasons for such actions by the Turkish authorities," the statement said. It said that "the lives and safety of the passengers were placed under threat" by the incident.
Also commenting on the plane's detention on Thursday, Syria's transport minister accused Turkey of "air piracy," Lebanon's al-Manar Television reported.
The channel quoted minister Mahoumd Said as saying the move amounted to "air piracy which contradicts civil aviation treaties." Turkish officials said they suspected the plane was carrying military equipment, and seized some of the cargo.
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