Cartagena, Colombia — Although President Juan Manuel Santos declared a summit of 30 nations from the Americas a success because thorny issues, including Cuba, were dealt with “frankness,” the leaders’ failure to reach agreement cast doubt on the future of such regional meetings.

On the sidelines of the summit, Santos and Obama held a bilateral meeting after which they announced May 15 as the date when a free trade agreement between the two countries will officially take effect.

The summit concluded Sunday with no formal declaration and no signing ceremony. However, Santos said the leaders had chosen to discuss behind closed doors “the issues that unite us as well as the issues that divide us in a sincere dialogue.”

Santos said that the majority of the countries represented at the summit, “support the participation of Cuba” in the summit process. President Barack Obama and Canadian Prime Minister Stephen Harper were alone in their opposition.

Santos announced that the next summit would be held in Panama in 2015 but countries of the ALBA bloc of Latin American nations — founded by Venezuela and Cuba in 2004 — announced Sunday they would not participate in another Summit of the Americas without Cuba’s inclusion. The bloc also demanded that the United States end its economic embargo of the island.

The ALBA bloc includes Antigua and Barbados, Bolivia, Dominica, Ecuador, Nicaragua, St. Vincent and the Grenadines. Haiti has observer status within the ALBA.

The presidents of Bolivia and Argentina left the meeting before it concluded Sunday, and the leaders of Venezuela, Ecuador, Nicaragua and Haiti did not show up.

Mexican President Felipe Calderón hailed the fact that discussions on Cuba and drug policy were even held, marking a “radical and unthinkable” difference with previous summits.

On drug policy, the leaders agreed to direct the Organization of American States to begin a thorough review of drug control policy in the region.

“We emphasized the possibility of exploring alternatives with consumer countries, ” said the president of Mexico, where nearly 50,000 people have been killed in the past six years in drug trafficking related violence. The OAS review, he said, will seek to analyze alternatives.

Eric Hershberg, director of the Latin American and Latino Studies at American University, said that an agreement to have the OAS look at the issue was a “step forward” in the U.S. position toward the issue. Obama said in a business leaders forum before the summit that a discussion on drug policy was “legitimate”.

Following the summit, Santos and Obama met privately at the Colombian presidential vacation home in this Caribbean coastal city, where they announced the implementation of the free trade agreement between the two countries.

U.S. and Colombian unions have opposed the trade deal, saying Colombia still has not cleaned up its record of human rights and labor rights abuses. The two countries signed a Labor Action Plan in April 2011 laying out steps the Colombian government needed to take to improve the rights of workers.

The National Labor School, an organization that tracks labor issues in Colombia, said in a statement that nine of the 37 measures laid out in the action plan had not been implemented. The others, the organization said, have been applied only partially. “There continue to be worrying situations of attacks on unionists and restriction to the right of association.”

Between April 7, 2011, when the action plan was signed, and April 13, 2012, some 28 union members have been killed, 10 have suffered attempts on their lives, two have been forcibly disappeared, and nearly 500 have received death threats, according to the National Labor School.

Obama’s visit to Cartagena was marred by a prostitution scandal involving 11 Secret Service men and five members of the military who formed part of the president’s security team in Colombia.

Obama said Sunday that the director of the Secret Service is investigating the scandal.

“I expect that investigation to be thorough and I expect it to be rigorous. If it turns out that that the allegations that have been made in the press are confirmed, then of course I’ll be angry,” Obama said in his first comments on the scandal, made during a press conference with Santos.

“We’re representing the people of the United States and when we travel to another country, I expect us to observe the highest standards, because we’re not just representing ourselves, we’re here on behalf of our people–and that means we conduct ourselves with the utmost dignity and probity. And obviously what’s been reported doesn’t match up to those standards.”