US Secretary of State John Kerry's attempts to build warmer relations with two US allies in Latin America may be hindered by reports of an American spy programme that widely targeted data in e-mails and telephone calls across the region.
Kerry is visiting Brazil and Colombia this week, his first trip to South America as the Obama administration's chief diplomat.
It comes at a time that disclosures by the National Security Agency whistle-blower Edward Snowden could chill talks on several fronts.
Those include trade and energy, and discussions about the October 23 state dinner that President Barack Obama is hosting for Brazil's president, Dilma Rousseff.
Kerry arrived late on Sunday in Bogota, the Colombian capital.
The country is holding peace talks to end a half century-old conflict with the western hemisphere's most potent rebel army, a force diminished in strength thanks in considerable measure to US military and intelligence support.
Kerry yesterday met Colombian officials negotiating with the nation's largest guerilla army to find peace in the South American country for the first time since 1964.
He was scheduled later to meet Colombia's president, Juan Manuel Santos, who said on Thursday that he wanted clarification from Washington on whether US intelligence-gathering in Colombia had overstepped the countries' joint operations against drug traffickers and illegal armed groups.
Santos said US Vice-President Joe Biden called him following Snowden's revelations, and offered him a series of technical explanations.
Asked if he was satisfied with them, Santos replied: "We are in that process." Biden called Rousseff to express what Brazil's communications minister, Helena Chagas, revealed was "his regret over the negative repercussions caused by the disclosures".
Biden invited Brazilian officials to Washington to get details about the programme. Rousseff told Biden that Brazil's sovereignty could not be infringed upon, and urged the US to change its security policies.
During Kerry's visit, the US wants to show its support for the peace talks between the Colombian government and the Revolutionary Armed Forces of Colombia, or Farc, which are taking place in Cuba.
Colombia is one of the United States' closest allies in the region, but the reports about the spying programme have rankled Colombian officials.
Brazil's O Globo newspaper reported last month that citizens of Colombia, Mexico, Brazil and others were among the targets of a massive operation to secretly gather information about phone calls and internet communications worldwide. Last week, Brazil's Foreign Minister Antonio Patriota was at the United Nations with counterparts from other South American nations to express their indignation about the spy programme to UN Secretary-General Ban Ki-moon.
Rousseff has faced protests since June which have weakened her domestic support.
But she could bolster her poll numbers with a strong stand against the US, said Carl Meacham, director of the Americas Programme at the Centre for Strategic and International Studies in Washington.
"The tone of the visit will be a bit tense because of these issues raised by the surveillance and I think Secretary Kerry will have to speak to that," he said.