The United States is investigating a rogue signal detected from Cuba which is thought to be blocking its satellite broadcasts into Iran.
Voice of America has just started broadcasting to Iran
The jamming was first discovered on 6 July when the government station Voice of America launched a daily Persian-language programme aimed at Iran's domestic audience.
The Los Angeles-based Iranian television network National Iranian TV (NITV) - which promotes reform in Iran - has also had its signal blocked.
"We are looking into the source of interference of these broadcasts and we'll be taking up with the Cubans the question of whether or not this interference is coming from Cuba," said US State Department spokesman Richard Boucher.
Iran saw widespread demonstrations last month against the conservative clerical establishment. Hundreds of reformers have been arrested and there has been a crackdown on the free press.
The signal is thought to come from a monitoring complex outside Havana set up by the Soviets during the Cold War to eavesdrop on the US.
US officials say Cuban President Fidel Castro could be in league with the Iranian government to stop Iranians from receiving satellite television.
"This action is illegal, represents a major threat to satellite communication and must be stopped," said Kenneth Tomlinson, chairman of the Broadcasting Board of Governors.
President of NITV Zia Atabay told the BBC that when Iranian students and writers come out of jail, the first thing they do is grab the phone to do an interview with the station, and invariably criticise their government.
He said they would continue to broadcast their message of the need for change in Iran in Australia and America.
Cold War jamming
But finding alternatives ways of reaching their key audience in Iran may be difficult for television stations, according to technical analyst Martin Peters from BBC Monitoring.
"They could change satellite but that is not necessarily the answer, as the audience would need to know about this, move their dishes and retune their receivers accordingly."
The chances of stumbling across the alternative transmission would be almost nil.
During the Cold War, Western broadcasters were constantly engaged in a game of cat and mouse with the Soviets in order to beam their programmes into the homes of ordinary Russians.
"In a co-ordinated effort, they would simultaneously use as many frequencies as possible because Russia only had so many transmitters for blocking," added Mr Peters.
"But given the current dish ban in Iran, those with fixed antennas will not want to draw attention to themselves by re-aligning theirs onto a new satellite."