An American researcher for the Congress said on Monday that he was barred from entering Iran for a security conference when his visa was rescinded at the last moment.

Kenneth Katzman, senior Middle East expert with the Congressional Research Service, which conducts research for Congress, said the fact that Iranians opposed to engagement with the United States had barred him from the event.

"Perhaps the anti-engagers threatened to have their people turn me back at Tehran airport. The conference organizers were forced by this pressure to back down and tell me not to come," local press quoted Katzman as saying.

Katzman was reportedly invited to the conference sponsored by the Iranian foreign ministry's think-tank and Tehran University.

Katzman said it was the first time a U.S. government representative had been invited to the conference, which focused on security in the Gulf. However, he found his visa had been rescinded while he was waiting for a connecting flight in Frankfurt airport.

The United States and Iran have severed diplomatic ties since Iran broke out Islamic revolution in 1979 and U.S. embassy personnel were taken hostage in a crisis that lasted 444 days.

The relations between the two countries are getting worse in recent years because of disputes over Tehran's nuclear ambitions and support for Islamic militants such as Hizbollah.

However, the Bush administration gave former Iranian President Mohammad Khatami an unrestricted visa to visit the United States early this month, including stops in New York, Chicago, and Washington for speeches and news conferences.

Source: Xinhua