(CNN) -- President Barack Obama is putting an international spin on his domestic economic agenda with planned trade talks at a weekend summit in Colombia, which is bringing together most of the hemisphere's leaders.
But separate security incidents -- one involving bomb blasts and the other the Secret Service -- overshadowed the start of the sixth Summit of the Americas in Cartagena.
Obama plans to focus on economy, trade, energy and regional security, and is also expected to highlight democratic and social reforms with 33 of the region's 35 leaders.
The president arrived in the Colombian coastal resort city Friday, a visit that will mark the most time a U.S. president has spent in that country, where security concerns had limited previous presidential trips.
Within hours of arriving, an undisclosed number of Secret Service agents traveling with the president were relieved of duty and replaced, said Edwin Donovan, an agency spokesman.
"There have been allegations of misconduct made against the Secret Service in Cartagena, Colombia, prior to the president's trip," Donovan said in a statement.
"Because of this, those personnel are being relieved of their assignments, returned to their place of duty, and are being replaced by other Secret Service personnel. The Secret Service takes all allegations of misconduct seriously."
Donovan declined to identify the nature of the alleged misconduct, saying only the mater was being turned over to the agency's internal affairs.
But Jon Adler, president of the Federal Law Enforcement Officers Association, told The Washington Post that the accusations relate to at least one agent having involvement with prostitutes in Cartagena.
CNN could not immediately confirm the claim.
Amid the reports that Secret Service agents were being replaced, two small blasts occurred nearly back-to-back in Cartagena.
The explosions, one near a bus station and another near a shopping mall, occurred well away from where the world leaders were gathering for the start of the summit, said Alberto Cantihho Toncell, a spokesman for the Colombia National Police.
There were no casualties, and only minor damage was reported, Toncell said.
The explosions came on the heels of a similar one earlier in the day near the U.S. Embassy in the capital city of Bogota, authorities said.
The blasts were a reminder of the violence that has gripped Colombia on-and-off as it battled powerful cocaine drug cartels. Violence has significantly fallen off in recent years as the Bogota government, aided by U.S. extradition efforts, has successfully picked apart the cartels.
Regional security, particularly the high price being paid in the drug war across Latin America, was expected to top the agenda for the leaders.
At a recent meeting at the White House with the leaders of Mexico and Canada, Obama was blunt about the ongoing threat in a region where some leaders believe the drug war is failing.
In an interview Friday with Colombia-based Caracol Television, Obama said he did not believe the answer was to legalize drugs, a consideration among some countries.
"I respect the fact that governments here are feeling very challenged by this, and what I want to do is have a constructive conversation about how we can partner with countries to solve that problem," he said.
"But I think it's a mistake to think that there is a silver bullet out there and that somehow legalization diminishes the broader challenge."
While enroute to Colombia, Obama announced the development of the Small Business Network of the Americas, which he said would help businesses gain access to markets south of the U.S. border.
But the agenda at the summit may be driven by other concerns that have long been debated by Latin American leaders.
Cuba, which is not a member of the Organization of American States, has not been invited to join the leaders, though there was a last minute move by Ecuador's leftist President Rafael Correa to get Cuban leader Raul Castro a seat at the table.
Correa's threat to organize a boycott with other leaders in the Bolivian Alliance (Venezuela, Bolivia and Nicaragua) led to intense diplomatic efforts behind the scenes. Inviting Castro could have caused problems for Obama, who is in an election year.
Obama told Caracol Television that what is preventing Cuba from being a "full member of the international community is not the United States of America," but rather Cuba's own policies.
"This remains a profoundly anti-democratic, authoritarian state," Obama said.
Colombian officials were aware of the potential fallout in this case, so the country's foreign minister was dispatched to Cuba. Colombian President Juan Manuel Santos flew to Cuba to meet with Castro.
Those meetings effectively ended the dispute, but Ecuador's Correa was angry. He fired off a letter to Santos criticizing the denial of Cuba's participation as "intolerable."
Then he boycotted the summit, even though the other leaders who had supported his appeal said they would attend.
During the previous summit three years ago in Port of Spain, Trinidad, Obama had an uncomfortable encounter with Hugo Chavez, when the Venezuelan leader handed him a book critical of the United States and Europe.
Chavez's attendance over the weekend remained uncertain Friday night, when he told Venezuelan National Television, "In reality, that won't be decided by me, but by the doctors."
In recent months, Chavez has been undergoing treatment in Havana for cancer.
Asked during the interview with Caracol Television whether the United States viewed Venezuela as a threat, the president was measured:
"We don't see Venezuela as a threat to the United States. I think that Venezuela has at times thrown its weight around in the neighborhood in ways that are destructive," he said.
"We don't think that the Venezuelan people have been served by rhetoric and, you know, the undermining of democratic institutions, the prevention of free speech or the fact that it's more difficult for the opposition to organize. We want the people of Latin America and the Caribbean to determine their own destiny."