A Syrian-bound plane intercepted by Turkey was carrying Russian-made defence equipment destined for Syria's defence ministry, Turkish Prime Minister Recep Tayyip Erdogan has said.
"Passenger aircraft cannot carry ammunition and defence equipment," Erdogan said, adding, "unfortunately there was such equipment on board", BBC reported.
Turkish jets forced the plane, coming from Moscow, to land in Ankara.
Syria and Russia have denied the plane was carrying illegal cargo.
They have accused Turkey of putting lives in danger.
The Syrian Air Airbus A320, with about 30 passengers on board, was intercepted on Wednesday evening by two Turkish fighters and escorted to the capital's Esenboga airport.
Turkey said previously it had received an intelligence tip-off that it had illegal cargo on board.
Speaking to reporters in Ankara, Erdogan said: "This was equipment and ammunition that was being sent from a Russian agency... to the Syrian Defence Ministry."
"Their examination is continuing and the necessary will follow," he added.
He said the supplier was the equivalent of Turkey's state-run arms supplier, the Mechanical and Chemical Industry Corporation.
Russia's state arms export agency Rosoboronexport had earlier said it had no information about the plane's cargo and denied it had any connection with the flight or anything on board.
Foreign Minister Ahmet Davutoglu has said Turkey is determined to stop any transfer of weapons to Syria through its airspace.
Tensions were already high between Turkey and Syria, following the deaths of five Turkish civilians by shelling from across the border last week.
Turkey has returned fire, and on Wednesday its top military commander warned Ankara would respond with greater force if the shelling continued.