A Syrian passenger plane forced to land in Turkey was carrying "illegal cargo", according to Turkey's foreign minister.
Ahmet Davutoglu said "objectionable" materials had been confiscated from the plane before it was allowed to leave.
Turkey sent jets on Wednesday to intercept the plane, which was en route from Moscow to Damascus, amid rumours it was carrying military equipment.
Tension between Turkey and Syria has been high since five Turkish civilians were killed last week by mortar bombs.
In response, Turkey fired into Syria for the first time since the uprising against President Bashar al-Assad began last year.
Mr Davutoglu did not specify whether any weapons had been found in an hours-long search of the plane.
"There is illegal cargo on the plane that should have been reported," he told the Anatolia news agency.
But unconfirmed reports in Turkish media said the confiscated cargo included boxes of military communication equipment.
The Airbus A320 airliner had about 30 passengers on board, far fewer than its 180 passenger capacity.
The foreign minister said the authorities would continue to investigate Syrian passenger planes flying over Turkish air space.
Russian officials said their Ankara embassy had asked the Turkish authorities for an explanation of the actions.
A source in Russia's arms export agency quoted by Interfax news agency denied there was any military equipment on board.
"Neither weapons nor any kind of systems or parts for military equipment were on board or could have been on board," the source said.
Earlier, Mr Davutoglu had said Ankara was determined to stop any transfer of weapons to Syria through its airspace.
He said Ankara had received information that the Damascus-bound plane could be carrying "non-civilian cargo".
The aircraft was escorted by two Turkish fighters to the capital's Esenboga airport for security checks.
It was allowed to take off at 02:30 (23:30 GMT on Wednesday), after several hours on the ground.
Meanwhile, the Turkish authorities have declared Syrian airspace to be unsafe and are preventing Turkish aircraft from flying over the country.