Brasilia  - Cuban President Raoul Castro, on his first official foreign visit since taking power in February, Thursday suggested that Havana and Washington could consider a possible prisoner exchange to start a thaw in relations between the two countries.

Castro, who took over leadership of the communist country in February from his ailing brother, revolutionary leader Fidel Castro, made the remarks after meeting Brazilian President Luiz Inacio Lula da Silva.

Castro was referring to the so-called Cuban Five, whose long prison sentences in the US for espionage and conspiracy to commit murder were upheld recently against two of the group.

Castro said it may be possible to exchange these Cuban "heroes" for political prisoners in Cuba - although it wasn't clear how serious he was.

"These prisoners (on Cuba) that everyone is talking about. They want us to let them go?" Castro replied to a question posed by journalists about the dissidents imprisoned in cuba. "We will send them with their families and all their belongings (to the US.) Then send us back our five heroes.

"We'll go about this gesture for gesture," Castro said.

Cuban dissidents in Havana responded that such a proposal was not viable, and it was impossible to compare people accused of acts of terrorism with political prisoners.

Lula made some of the most pointed remarks yet in his steady support of Cuba, demanding that US president-elect Barack Obama name the reason for the continuing economic boycott of the Caribbean island.

The only thing Cuba did wrong was "winning its own freedom," Lula said.

The US put the blockade in place in 1962 in the midst of tensions over Soviet involvement with the island that brought the world to the brink of World War III.

"The United States should explain the reason for this blockade," Lula said. "It's the United States which must make a gesture, since they erected the blockade, and that gesture must be declaring an end to the blockade."

Castro earlier this week was greeted like a long-lost son at a major Latin American summit in a Brazilian coastal resort amidst a growing, unified campaign across Latin America to convince the US to end its blockade as Obama prepares to take office January 20.

The push also comes ahead of the January 1 celebration of Cuba's 50th anniversary of the communist revolution.

Obama, a Democrat, has indicated his intention to push for more direct diplomacy with countries which have been shut out of US diplomatic contacts during the eight years of US Republican President George W Bush.

The Cuban Five were arrested in late 1998 in Miami and are currently in prison in the United States. The US has charged that they sent Cuba information that led to two civilian planes being shot down, lied about their identities, tried to infiltrate the US Southern Command headquarters in West Miami-Dade, Florida, and sent Cuba classified information. (dpa)