The Cuban Government has denied that it is intentionally jamming an American satellite TV broadcast to Iran.
Voice of America has just started broadcasting to Iran
"Cuba has never undertaken nor will it ever undertake these types of interruptions in US television satellite transmissions," a Cuban Foreign Ministry statement said.
However, officials promised to bow to US requests that they investigate whether signals originating in Cuba could be unintentionally interfering with the broadcasts.
Last week the US said it was investigating a rogue signal detected from Cuba.
The foreign ministry statement did admit that Cuba routinely does block some broadcasts - notably the US-funded Radio and Television Marti, beamed to Cuba itself.
The jamming was first discovered on 6 July when the government-funded 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.
"Cuba, within its rights, has interfered, interferes and will continue to interfere only the illegal transmissions of radio and television that the government of the United States makes to our country," the statement said.
"We do so with the sovereign right to defend our
broadcast air space from the subversive radio and television aggression that, violating international law from the first years of the revolution, have been carried out by the American government," it added.
On Friday US State Department spokesman Richard Boucher said that the interference appeared to be intentional.
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.
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.
US officials say Cuban President Fidel Castro could be in league with the Iranian government to stop Iranians from receiving satellite television.
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.