ISTANBUL - An Iranian cargo plane was forced to land in southeast Turkey for the second time within a week on suspicion it was carrying weapons or bomb-making material to Syria, Turkish media reported on Sunday.

Related readings:  Iran sends rocket, capsule into space  Iran plans to sell its nuclear materials  Russian Foreign Minister calls for resumption of Iran nuclear talks  Iran warns West against military intervention in Libya

The plane which took off from Tehran landed overnight at Diyarbakir airport and searches took place on Sunday, broadcaster CNN Turk said.

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 UN nuclear watchdog is probing allegations of covert atomic activities in Syria. Iran and Syria, close allies, deny ever harbouring nuclear weapons ambitions.