Former U.S. President Jimmy Carter is in Cuba where he is challenging the Bush administration on its accusations that Fidel Castro is developing biological weapons. Jimmy Carter says U.S. officials who briefed him before this trip told him they had no evidence that Cuba is exporting weapons technology.

White House spokesman Ari Fleischer says the issue did not come up in Mr. Carter's briefing with National Security Advisor Condoleezza Rice because the trip's focus is more on human rights. But Mr. Fleischer made it clear the Bush administration does believe Cuban President Fidel Castro is developing biological weapons.

"The issue about Cuba engaging in biological warfare research and development is an issue of concern to the United States," he said.

U.S. Under Secretary of State John Bolton last week said Cuba has at least a limited biological warfare program and is sharing that technology with countries hostile to the United States, such as Libya and Iran.

Touring Cuba's Center for Genetic Engineering and Biotechnology Monday, President Carter said those in Washington who are concerned about the laboratories should inspect them personally. Accompanied on the tour by President Castro, Mr. Carter suggested the timing of the controversy over biological weapons was intended to cast a shadow over his private, goodwill visit.

Mr. Fleischer says President Bush supports the trip and hopes Mr. Carter is able to help bring more democracy to Cuba.

"The president believes that President Carter has been a champion of human rights around the world," he said. "And President Carter will be in Cuba for a number of days, and the president wishes President Carter every bit of success in helping convince President Castro to change his regime, to change his tyrannical system, to bring freedom and to end the repression of the Cuban people."

There are no formal diplomatic relations between the United States and Cuba. Mr. Carter is the first U.S. president in or out of office to visit the island since Mr. Castro seized power in 1959.

President Bush is expected to make a major speech on U.S.-Cuba relations next Monday before traveling to Miami for attend a fundraiser for his brother, Florida Governor Jeb Bush.