The plane which took off from Tehran landed overnight at Diyarbakir airport and searches took place Sunday.
The second plane to be grounded en route from Iran to Syria in Diyarbakır
within one week was found to contain a BIXI machine gun. The weapon has been confiscated and the reason for its presence will be investigated.
Last Tuesday night another plane was similarly forced to land at Diyarbakir but departed the following day after a search squad trained in chemical, biological, radioactive and nuclear cargo found nothing illegal.
Turkey's Foreign Ministry and airport authorities declined to comment. A ministry spokesman said after last week's plane grounding the search was routine.
Turkish media suggested the plane may have been stopped at the request of the United Nations to investigate whether it was carrying nuclear material.
The U.N. nuclear watchdog
is probing allegations of covert atomic activities in Syria. Iran and Syria, close allies, deny ever harboring nuclear weapons ambitions.