James Cason, the top US diplomat in Havana, said in a statement on Friday the United States has no reason to attack Cuba and no plan to do so.
In the past few weeks, Castro, leader of the only one-party communist government in the Americas, said State Department officials made "direct threats at Cuba" that might include plans for an invasion or possibly plans to assassinate him.
Cason, who leads the US Interests section there in the absence of a US embassy, said Castro's charges were made up to try to sow fear in the population and to justify continued use of vast military, security and intelligence apparatuses.
In recent months the Cuban government has begun a steady drumbeat ahead of a potential US invasion, holding neighbourhood watch seminars and even advising people on evacuation centres in case of war.
Americans stay away
A crackdown by the Bush administration on US travel to Cuba has reduced the number of non-Cuban Americans visiting the island to a trickle, travel agents and Cuban officials have said.
"It (cancellation of the cultural exchange travel licences) had a tremendous impact on the flow of people. Business is down by 30 per cent"
Cuba Travel Services president
At Havana's Hemingway Marina, it is hard to find a yacht or big-game fishing boat with a US flag these days.
"The Commerce Department began asking for export licences," said the marina's commodore, Jose Miguel Diaz.
"The yachters didn't want trouble."
Havana was packed with American tourists in November and December, including museum curators and retired academics, who rushed to get a glimpse of the communist-run nation before permits for cultural and educational visits ended.
The so-called people-to-people licences were introduced by the Clinton administration as a way of increasing US contacts
with the Cuban people with a view to encouraging democratic
change under Castro's government.
But that doorway to Havana slammed shut on 31 December after President George Bush cancelled cultural exchange travel licences, as he tightened sanctions against Castro.
"It had a tremendous impact on the flow of people. Business is down by 30 per cent," said Michael Zuccato, president of Cuba Travel Services, which operates charter flights to Cuba from Los Angeles and Miami.
"There is more fear among Americans about travelling to Cuba," said a European tour operator in Havana who had cancellations by US customers.
Last year 160,000 US citizens made authorised visits to Cuba, 85% of them Americans of Cuban descent, who can visit relatives on the island once a year.
The remainder travelled on special permits for business, cultural, academic and religious trips.