WASHINGTON (AFP) - A charter plane carrying about 100 people including Americans was diverted to Iran on Friday during a flight from Bagram air base in Afghanistan, US officials said.

But a State Department official denied the Iranian military had forced down the flight operated by Fly Dubai, saying the plane was re-routed due to a "bureaucratic issue." "Contrary to press reports, this plane was not forced down by the Iranian military," the State Department official said.

"The issue appears to have been resolved and hopefully the plane will be able to take off soon," the official said.

Washington and Teheran have not had formal diplomatic relations for three decades, since the 1979 storming of the US embassy in Teheran and the subsequent 444-day hostage crisis.

In recent months, the two countries have been holding face-to-face negotiations on Iran's suspect nuclear program, but ties remain tense.

And several Americans are being held by Teheran despite pleas from Washington to send them home.

It was not immediately clear who was on board the Fly Dubai plane, and it remained uncertain if there were any US troops on board flying from the sprawling Bagram military air base just outside Kabul.

Officials confirmed however that among about 100 passengers on board, there are American citizens as well as other US government contractors of different nationalities.

"We are still checking who was on the flight," a defense official, who spoke on condition of anonymity, told AFP.