The US on Tuesday refused to back down from Bush's charge that Cuba is a favoured destination for paedophiles and other sex tourists after Castro angrily denied the claim in an invective-filled speech.
"The issue of prostitution in Cuba is something, I think, that is well-documented," deputy State Department spokesman Adam Ereli said.
He referred to a 2002 report from a Washington-based human rights group, The Protection Project, that said Cuba had replaced Southeast Asia as one of the world's top sex tourism destinations, and the State Department's own annual Trafficking in Persons reports.
Cuba denies encouraging the sex trade, and on Monday Castro lashed out at Bush, calling the accusations "crude calumnies" made by "a sinister character who threatens and insults us" and pointing to the US president's past problems with alcohol.
Castro questioned his mental capacity, quoting from the book, Bush on the Couch, to describe the US president as a past alcoholic. About half of the 90-minute speech was devoted to quotes from the book, written by psychoanalyst Justin Frank, who portrays Bush as a man driven by rage and fear.
State Department spokesman Ereli said he had not seen those specific comments, adding that he declined to "dignify them with a response". However, the US would continue to press for democratic transition in Cuba despite Castro's complaints, he said.
"It's in the interest of the Cuban people and in the interest of the hemisphere to help hasten transition to a democratic Cuba and that's what the policy of the United States is directed to," Ereli said.
The 2004 edition of the State Department report released in June, slams Cuba for failing to take action against the sex trade, particularly involving children.
"The dictator welcomes sex tourism," Bush said. "Sex tourism is a vital source of hard currency to keep his corrupt government afloat."