Cuban President Fidel Castro has dismissed as "absurd" and "malicious" a US magazine report saying he had amassed a personal fortune of $900m.
Fidel Castro says he has no personal fortune
Mr Castro said the estimate, published in Forbes magazine, was part of a US campaign to discredit him.
He said if anyone found evidence that he had even "a single dollar" in a foreign bank account, he would resign.
The survey assumes Mr Castro has economic control of state enterprises and receives a percentage of profit.
In an article published earlier this month, Forbes ranked Fidel Castro's fortune as seventh largest in a list of the world's wealthiest monarchs and dictators - higher than the UK's Queen Elizabeth II.
In a live television programme lasting four and a half hours shown on Monday, Mr Castro told Cubans the story was a "repugnant slander" by a capitalist publication.
"If they can prove that I have a bank account abroad, with $900m, with $1m, $500,000, $100,000 or $1 in it, I will resign," he said at the end of the broadcast.
"It is so ridiculous to say I have a fortune of $900m, a fortune with no heirs. What would I need all that money for, if I will soon be 80 years old?"
Lying on the desk in front of him was a copy of the magazine which is not available in Cuba.
Mr Castro said the article within it, entitled Fortunes of Kings, Queens and Dictators, had been quoted so many times by media around the world that it had become dogma.
As part of his response, he gathered evidence from a series of high-ranking Cuban officials.
The head of the country's central bank declared that it would be totally impossible for anyone in the Cuban leadership, least of all Mr Castro, to have foreign bank accounts.
Forbes magazine had written about rumours of large stashes in Switzerland.
On Tuesday, Forbes said it stood by its "statement and valuation" and had reliable sources on the story.
"One thing that Castro brought up was the fact that he did not have bank accounts outside Cuba. Just to be clear, the Forbes article states that it has not taken into account any money rumoured to be held in Swiss bank accounts," a company statement said.
Last year, Mr Castro threatened to sue Forbes after the magazine included him on its 2005 list with an estimated fortune of $550m, Reuters news agency reports.
Diplomats and businessmen in Havana, who have had close access to Mr Castro, do tend to concur that avarice is not one of his vices, says the BBC's Stephen Gibbs in Havana.
Most say his personal life is notable for its austerity, our correspondent adds.