President Fidel Castro has denied US allegations that Cuba is trying to develop biological weapons.
The Cuban leader challenged US authorities to offer evidence to back up the allegations.
In a live television broadcast, he called on US officials to "present even the most minimum proof", adding that it was impossible because such evidence "does not and cannot exist".
Mr Castro's speech was the Cuban government's first detailed response to the allegations by US state department undersecretary Mr John Bolton.
"No-one has ever presented a single shred of evidence that our homeland has conceived a programme that develops nuclear, chemical or biological weapons," Mr Castro said.
"The doors of our institutions are open...Cuba has absolutely nothing to hide."
He added that Cuba opposes terrorism, saying that any Cuban scientist found working on biological weapons for transfer to other countries would be tried for treason.
He also noted that Cuba publicly condemned the September 11th terrorist attacks the day they happened.
Mr Castro went on to say that in the 43 years since the Cuban revolution, his country had never launched a terrorist attack on the US, even though "thousands of compatriots" had been killed in terrorist attacks launched from American soil.
AP