An Iranian news agency said on Tuesday that a US military aircraft had unintentionally violated Iranian airspace and been forced to land in Iran, but later allowed to leave.

The semi-official Fars News Agency did not say when the incident happened or give a source for the report, which comes at a time of tension between Tehran and Washington over Iran's disputed nuclear programme.

The news agency said five senior US military officials had been interrogated at an Iranian airport and released a day later after it became clear the plane had not entered Iranian airspace intentionally.

'After it became clear that they unintentionally entered Iran's air space and their destination was Afghanistan, they were allowed to leave Iran for Afghanistan,' Fars said.

In Washington, the Pentagon said it was unaware of any US warplanes being forced to land in Iran and that all US aircraft in the Gulf region were accounted for.

In an initial report, Fars described the aircraft as a warplane. But later it simply called it a 'Falcon', giving no further details. - Reuters