Castro (right) and Chavez are the best of friends

The hosts of "The Morning High Jinks" on WXDJ-FM edited tapes of an earlier hoax involving Venezuela President Hugo Chavez to get through to Mr Castro.

After a brief conversation, the Spanish-speaking hosts broke in to reveal the prank and called Mr Castro a killer, prompting a tirade of abuse.

WXDJ has 30 days to pay or appeal.

The station had argued that people in Cuba were exempt from a rule requiring that people be notified before their voices are used on air.

The Federal Communications Commission rejected this, saying the residence or political status of the target of the joke was irrelevant.

"It was in fact the intention and result of WXDJ's actions to fool and surprise the recipients of the call," the commission notice said.

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They then exchanged pleasantries with Mr Castro before telling him he had fallen for a hoax and calling him a killer.

The conversation ended with a stream of abuse from Mr Castro.

Six months earlier, in a similar prank, they managed to fool Mr Chavez into thinking he was speaking to the Cuban leader, before launching into a diatribe against him. Unlike Mr Castro, he hung up.

Miami malice

It is not known whether WXDJ faced any penalty for that incident.

The radio station has 30 days to pay the fine or file a statement explaining why it should be reduced or cancelled.

The friendship between Mr Chavez and Mr Castro is well-known.

Miami, meanwhile, is home to a large expatriate Cuban population, much of it vociferously anti-Castro.