AFP - Cuba and Venezuela, as well as the United States, need to show "not simply words but also deeds" if they are to thaw their relations, US President Barack Obama said Sunday.

While noting the "positive signs" in Washington's relationships with the two hostile Latin American states, Obama, speaking at the close of a Summit of the Americas, said they had to be backed up by action.

"The test for all of us is not simply words, but also deeds," he said.

Specifically on Cuba, Obama admitted that Washington's half-century-old policy on the communist island "hasn't worked the way we want it to; the Cuban people aren't free."

But that policy will not be changed "overnight," he said.

"Issues of political prisoners, freedom of speech and democracy are important, and can't simply be brushed aside," he said.

Obama's comments tempered speculation that a historic thaw in relations between the United States and Cuba -- and with Cuba's chief ally Venezuela -- was on its way following conciliatory gestures by all three countries.

Obama and Cuban President Raul Castro in recent days said they were willing to open talks on such hot-button issues as political prisoners and human rights.

And Venezuelan President Hugo Chavez went out of his way during the summit to shake Obama's hand several times and to give him a book about Latin America and its exploitation by big powers through the centuries.

Still, Chavez and many other Latin American leaders at the summit railed at Cuba being the only country from the region to be excluded.

They also pressed their demand that the US embargo on Cuba be lifted.

Obama, though, repeatedly said that the only way the United States would make more concessions to Cuba would be if Raul Castro first made concrete policy changes. He also acknowledged half a century of animosity and mistrust would not be quickly set aside.