State Department spokesman Sean McCormack said a three-person US assessment team was on stand-by to go to Cuba to see what was needed after Wilma flooded Havana and western shore areas this week.
US aid would be funnelled through a non-governmental organisation if it were needed, he said, adding that Washington had sent a diplomatic note to Cuba on Tuesday offering help and received a positive response a day later.
Havana's reply to the US offer, read out by Castro on a live television broadcast, said Cuba had not requested international aid. "That is not an acceptance of aid," the Cuban leader said.
Castro, annoyed that Washington was distorting Cuba's intentions, said Havana had only accepted a visit by the assessment team in an effort to build regional co-operation in dealing with the growing danger posed by hurricanes.
"We have no objections at all to the three officials visiting us, to know their assessment and exchange views on these matters," Castro said. "We won't close the door."
Two months ago the United States did not take up Havana's offer to send more than 1,000 doctors and tons of medical supplies to the United States after Hurricane Katrina hit the US Gulf Coast. Cuba said the United States never formally responded to the offer for political reasons, but State Department officials said the help was not needed.