Ailing Cuban leader Fidel Castro took on front-running U.S. Republican presidential candidate John McCain on Monday, accusing him of lying about Cubans torturing American prisoners of war in Vietnam.

At a campaign stop in Miami last month, the Arizona senator told anti-Castro exiles that American POWs held with him in Hanoi were tortured by "a couple of Cubans."

"His accusation against the Cuban revolutionaries ... are completely unethical," Castro wrote in an article published by the ruling Communist Party newspaper Granma.

"The commandments of the religion you practice prohibit lying," he said of McCain, who was raised an Episcopalian and calls himself a Christian.

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McCain, a Navy pilot when he was shot down over North Vietnam in 1967, says he was tortured by his Vietnamese captors over more than five years in captivity. Cuba and North Vietnam were Cold War allies of the Soviet Union at the time.

McCain has vowed to keep up decades-old U.S. pressure for political change in Cuba's one-party state. That has included a travel ban and trade and financial sanctions enforced a few years after Castro's 1959 revolution on the Caribbean island, which lies just 90 miles from the U.S. coast.

Castro's criticism brought a sharp retort from McCain as he campaigned in Annapolis, Maryland.

"For me to respond to Fidel Castro, who has oppressed and repressed his people and who is one of the most brutal dictators on Earth, for me to dignify any comments he might make is certainly beneath me," he said at a press conference.

"It's a matter of record and you can ask several of the POWs who had direct contact with some, some thug that came to Hanoi with an underling assistant."

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