HAVANA - Talks toward a thaw in U.S.-Cuba relations seemed to be a real possibility after the new presidents of both countries reached out to each other with surprisingly straightforward language about their desire to revive a relationship frozen by 50 years of cold war.

Barack Obama said Thursday it was up to Havana to take the next step after his "good faith" gesture of removing some of the restrictions that lock Americans and their money out of Cuba.

Raul Castro responded within hours, saying "we have sent word to the U.S. government in private and in public that we are willing to discuss everything human rights, freedom of the press, political prisoners, everything."

"We could be talking about many other things," Castro replied from a summit in Venezuela. "We could be wrong, we admit it. We're human beings."

It was the most conciliatory language Castro or his brother Fidel who handed him the presidency a year ago after falling ill have used with any U.S. administration since that of Dwight D. Eisenhower in early 1961, when the nations broke off relations. It appeared to be a transcendent development, the best opportunity for talks in a half-century.

Raul Castro has previously said he would be willing to discuss all issues with Obama. But Cuban officials have historically bristled at the suggestion that they might discuss human rights or political prisoners with the Americans, saying such matters are none of the Yankees' business.

Castro called on the U.S. to release five Cubans imprisoned on espionage convictions and offered to free a group of political prisoners in exchange.

Talking about these issues, of course, is no guarantee Havana is ready to offer the reciprocity Obama says the U.S. needs to see before making any more changes in its Cuba policies.

Indeed, Obama said a relationship frozen for 50 years "won't thaw overnight."

But their words seemed as historic as any that leaders of the two nations have made to one another.

Relations warmed briefly during Jimmy Carter's administration, which featured short-lived direct flights between Miami and Havana and the opening of interests sections that provide some contact in lieu of embassies. But that honeymoon soon ended with a refugee crisis when 125,000 Cubans fled to the United States from the Mariel port west of Havana in 1980.

Warming relations under Bill Clinton also were put in the freezer after Cuban fighter jets shot down two civilian planes off the island's coast in 1996, killing the four exiles aboard.

Raul Castro said his only conditions for talks now are that Washington treat them as a conversation between equals and respect "the Cuban people's right to self-determination."

Earlier this week, Obama lifted restrictions on visits and money sent to Cuba by Americans with families there steps he called "extraordinarily significant" for the families. But he ruled out a unilateral end to the U.S. trade embargo against Cuba, even though the policy is widely seen as a failure that has complicated U.S. relations throughout Latin America and the Caribbean.

On a visit to Mexico City, Obama said the Cuban government needs to reciprocate with actions "grounded in respect for human rights," possibly including lifting its own restrictions on Cubans' ability to travel and to voice their opinions.

President Castro did not mention Obama's comments specifically and stopped short of promising any action.