South American leaders have pressed President Barack Obama to end the U.S. economic embargo of Cuba and abstain from interventionist policies as he attempts to reshape America's hemispheric relations.  Mr. Obama is attending the fifth Summit of the Americas in Port of Spain, the capital of Trinidad and Tobago.

Ahead of the summit's first plenary session, President Obama met with heads of the 12-member Union of South American Nations, UNASUR.

Mr. Obama made brief comments before the meeting began.

"UNASUR is doing some excellent work in integrating efforts in the region around things like energy and security. I have a lot to learn," he said.

A senior U.S. official who attended the meeting said Mr. Obama expressed a desire to work with UNASUR nations to confront economic, environmental, and energy challenges.

The official said more than one leader pressed Mr. Obama to end the decades-old embargo of Cuba. Mr. Obama is said to have declared that the United States and Cuba are "on a path of change", while reminding his fellow heads of state that the democratic process that brought them into office does not exist in Cuba.

The U.S. official said several UNASUR leaders detailed what they see as a long history of U.S. intervention in their countries. Venezuelan President Hugo Chavez presented Mr. Obama with an academic book on precisely that subject.

President Obama is said to have stated that, while the past must be understood, he is not there to argue history - and that it is time to "move on" to confront today's challenges.

Saturday's Obama-Chavez encounter was the second of the summit, and provided another opportunity for a handshake between the two men. Mr. Obama was asked  what he said to the fiery critic of the United States during their first handshake.

"I said, 'como estas?' [How are you?]" he said.

At Friday's opening ceremony, several leaders noted past grievances with the United States while also expressing hope for a more productive and respectful relationship under President Obama.

Argentine President Cristina Fernandez de Kitchner said that the United States has a president named Barack Obama, a product of change in his country that mirrors changes in other countries. She said many of today's leaders in Latin America, like President "Lula" da Silva of Brazil or President Evo Morales of Bolivia, could never have been elected in previous decades.

The summit's schedule includes three plenary sessions before a final declaration is issued Sunday. Venezuelan President Chavez  threatened to refuse to sign the declaration to protest Cuba's absence from the hemispheric gathering, and to protest the document's failure - as it is now reportedly written -  to demand an end to the U.S. embargo of the island.