Richard Boucher told reporters the State Department had put the request through Cuban interest sections in Washington.

"We would expect to hear back from them," he added.

Another senior official said: “We’re giving them a chance to find it (the jamming station) and close it down.”

Government and company statements on Wednesday said the jamming came from a location close to the Cuban capital Havana and was affecting both US government and private satellite television broadcasts aimed at the opposition in Iran.

Officials from Cuban interests were unavailable for comment.

If confirmed, it would be a case of cooperation between two ideologically distinct governments - both of which Washington dislikes.

The government-funded Broadcasting Board of Governors said this week the jamming began at about the same time as it started a daily news programme for Iranians on 6 July.

The Los Angeles-based Iranian television network National Iranian TV (NITV) - which promotes reform in Iran - has also had its signal blocked, though they noticed problems on 5 July

NITV officials asked a specialist company, TLS Inc., to find the source of the jamming.

"TLS investigations concluded an ellipse of the most probable location of the source of the interference, which it identified as being in the vicinity of Havana," the company said in a statement posted on its Web site.

The jamming coincided with opposition preparations for protests planned for 9 July, the fourth anniversary of a raid on a Tehran University dormitory.

Some protests took place on 9 July, but they were much smaller than the opposition and their supporters in the United States had hoped.