The plane, instructed to land at Diyarbakir airport as it over flew eastern Turkey on its way to Syria, was found to be carrying 150 tons of food but no" material contrary to international standards," the sources added.

After several hours of search on the plane for military or nuclear related cargo onboard, the aircraft took off at 1330 GMT, an AFP correspondent at the scene saw.

Anti-nuclear, biological and chemical material unit of civilian defence teams took part in the inspection of the plane as well, Anatolia news agency reported.

The UN nuclear watchdog agency has been probing allegations since 2008 that Syria had been building an undeclared reactor at a remote desert site called Dair Alzour until it was bombed by Israeli planes in September 2007.

Damascus granted UN inspectors one off access to the site in June 2008 but no follow up visits to either Dair Alzour or other possible related sites since then.

Earlier this month, the head of the Vienna based International Atomic Energy Agency, Yukiya Amano, complained that Syria "has not cooperated with the agency since June 2008."

The Iranian plane took off from Tehran on Tuesday night bound for the Syrian city of Aleppo.

It landed in Turkey upon order of Turkish foreign ministry, security sources said.

Two Turkish F-16 fighter planes were put on standby to intervene if the Iranian plane did not obey the orders of Diyarbakir airport officials, the same sources said.

However, a Turkish diplomatic source told AFP that the plane's landing was a "routine" practice.

The plane was allowed to continue for its destination, as no extraordinary situation occured during the "regular" search, the Turkish foreign ministry spokesperson Selcuk Unal said, Anatolia reported.

On Tuesday, Israeli naval commandos operating deep in international waters boarded a ship carrying arms allegedly on their way from Iran to Palestinian militants in the Gaza Strip.

Israel said the Panamanian-flagged ship had sailed from the Turkish port of Mersin and was heading for Alexandria in Egypt, but that the arms originated in Iran.

The Israeli military said it believed the weapons were loaded in the Syrian port of Latakia, and stressed that Turkey was in no way involved.

The UN Security Council has imposed sanctions, including an arms embargo, on Iran over its refusal to halt its uranium enrichment programme which the West suspects hides a drive to build nuclear weapons.

Tehran denies the charges and insists its nuclear program is solely geared toward electrity generation.