Cuba is open to talks with the United States about "everything" including political prisoners, President Raul Castro said on Thursday, a major softening of the communist island's stance toward its long-term foe.

"We have sent messages to the US government in private and in public that we are willing to discuss everything, whenever they want," Mr Castro said in an impassioned speech to a meeting of leftist leaders in Venezuela on the anniversary of a failed US-led invasion of Cuba in 1961.

"Human rights, press freedom, political prisoners, everything, everything, everything they want to talk about," he said, insisting only that the talks be on equal terms and without challenging Cuba's sovereignty.

In Washington, US State Department spokesman Robert Wood welcomed Mr Castro's latest comments but repeated that Cuba must release political prisoners, among other moves.

He avoided referring to conditions being met for talks to start, but made clear Washington expects Havana to take actions.

"If indeed those reports are true, I think that is a positive step. But again, as the secretary (of State Hillary Clinton) said, we urge Cuba to release political prisoners, to allow for the free flow of information and freedom of assembly," said Mr Wood yesterday.

"If the Cuban government's interested in having a substantive, serious dialogue with the United States, it needs to address not just concerns of the United States and other countries, but of the Cuban people," Mr Woods said.

Cuba is said to have about 200 political prisoners, whom it considers mercenaries for the United States. It also severely limits freedom of expression, puts limits on foreign travel by its citizens and does not hold multi-party elections.