Leaders from across the Americas were to wrap up a two-day gathering here Sunday with US President Barack Obama under intense Latin American pressure to let Cuba attend future hemispheric summits.
Saturday, Colombian President Juan Manuel Santos, the host of the Summit of the Americas and Washington's closest ally in Latin America, said it would be "unacceptable" to keep Cuba out of the next gathering.
And a closed-door plenary session produced a "frank discussion" on the issue, according to Peruvian Foreign Minister Rafael Roncaglio. "Now we are seeking a final statement for the summit and it is up to the Colombian president to do it.
"The isolation, the indifference has shown its ineffectiveness. In today's world, there is no justification for this anachronism," Santos said on the summit's opening day.
Cuba has never taken part in a Summit of the Americas, a regular meeting sponsored by the US-based Organisation of American States (OAS).
The Colombian's leader's statement was echoed by remarks by his Bolivian counterpart, Evo Morales, who argued that all Latin American states backed Cuba's participation in the summits.
"It is just impossible for one country to oppose the will of others and not listen to them." the Bolivian president said.
But despite the intense pressure, a deal on the issue appears unlikely, with the United States backed by Canada refusing to yield.
Obama, who is campaigning for re-election in the November election, cannot afford to give ammunition to his domestic right-wing opponents who reject any concessions to a communist regime seen as violating the democratic and human rights of its people.
Havana's exclusion also prompted Ecuador's Rafael Correa to stay away.
And an alliance of left-leaning Latin American countries known as ALBA announced here that its members would not take part in any future summits of the Americas if Cuba was not included.
In a statement, ALBA also demanded an immediate end to Washington's 50-year-old "inhuman economic, trade and financial embargo against Cuba" and urged regional countries "to continue to maintain its united solidarity in favour of Cuba's admission to the summit."
ALBA groups Venezuela, Ecuador, Bolivia, Nicaragua, Cuba, Antigua and Barbuda, and Saint Vincent and the Grenadines, said in a statement.
Meanwhile, several Central American leaders met here on the sidelines of the summit Saturday to discuss Guatemala's proposal to consider legalising street drug consumption. But they failed to reach consensus.
The proposal was to be taken up by hemispheric leaders at a private session later Sunday.
Obama told his peers he favoured a debate on a new drug war strategy but opposes decriminalisation or legalisation of drugs.
The leaders were to set to sign the summit's final statement before giving a press conference.
The text focuses on poverty eradication, regional integration, transitional crime and increased access to technology, but is likely to leave aside controversial issues such as Cuba, the drug fight and Argentina's claim on the Falklands.
Obama was also to have a bilateral session with Caribbean leaders before attending a working lunch with Santos.
The two leaders were then to give a joint press conference before Obama's departure for home.
Santos also scheduled bilateral talks with Brazilian President Dilma Rousseff.
Obama was later to join Santos at a ceremony in Cartagena's historic center to deliver land titles to descendants of African runaway slaves for more than 3350 hectares (8200 acres) of nearby ancestral land that they occupy.
Cartagena was the most important port for the slave trade during Spanish colonial rule.