"Not including Cuba in such an important summit where all the other Latin American and North American countries are included is another reason."
Thirty-four countries, including the US, are attending the summit of North and Latin American nations which is due to wrap up on Sunday in Port of Spain, the capital of Trinidad and Tobago.
Cuba is barred from the summit because it is not considered a democracy by organisers. Latin American leaders have urged the US to drop its 47-year trade embargo against the country.
Hugo Chavez, the Venezuelan president, had declared as early as Thursday that he condemned Cuba's exclusion and that he would not endorse the draft declaration.
But the mood at the summit remained upbeat and cordial.
Luis Inacio Lula de Silva, the Brazilian president, praised Barack Obama, the US president, and Chavez, saying that they were good men.
"[Silva was] trying to promote better relations between both countries," our correspondent reported.
"He even walked to Obama and said to him 'don't listen to your advisers when they talk to you about Chavez - Chavez is a good man and this is a very good opportunity'.
"There is a lot of optimism and flirting between even Chavez and Obama. But we don't know if this is going to make a real difference on the ground."
Chavez has been a vocal critic of US policies in the past.
|Obama's visit was welcomed by
many in Trinidad and Tobago [Reuters]
At the beginning of the talks on Friday, Obama said that Washington would seek a "new beginning" with Cuba, which has a communist government.
"I know there is a longer journey that must be travelled in overcoming decades of mistrust," Obama said.
"But there are critical steps we can take toward a new day."
The US has already dropped restrictions on Cuban-Americans visiting relatives in Cuba and is permitting US companies to bid for telecommunications licences.
Raul Castro, the Cuban president, has said his country is open to talks with Obama on "everything", including human rights, press freedom and political prisoners.
The US president also said that he would seek an "equal partnership" with Latin American states during his administration.
Colin Harding, a Latin American analyst, told Al Jazeera that Obama was aiming to show a departure from the previous government of George Bush.
"President Obama is very much trying to change the mood music," Harding said.
"He wants to show that there is a new administration with a new outlook. He is prepared to listen and to learn and to treat the Latin Americans as equal and not as some kind of a younger brother."
The weekend-long summit is nominally to discuss regional security and the global financial crisis.
However, many of the leaders see Cuba as a priority and argue that efforts by the US to marginalise the state are obsolete and have instead only isolated the US government in the region.
The fifth summit of the Americas is the first to be held in the Caribbean.