Costa Rica's President Laura Chinchilla came under pressure on Tuesday after the government admitted she had used a private jet owned by a foreign oil company, prompting an investigation by the attorney general's office.
Communications minister Francisco Chacon told reporters Chinchilla had taken the jet, paid for by Colombia-based oil company THX Energy, last weekend to Peru to attend a wedding and meet Peruvian President Ollanta Umala.
She also used a plane paid for by the firm to attend the funeral of the late Venezuelan leader Hugo Chavez, he added.
"There's no conflict of interest here. The fact there are companies working with the government to provide, as a contribution, certain services is not new to this administration," he said, without elaborating further.
However, the attorney general's office said it was investigating whether Chinchilla had broken the law by using the seven-seat Cessna 525B Citation CJ3 aircraft.
The president of Costa Rica has no plane. Chinchilla usually flies on commercial airlines or uses planes provided by other governments when making state visits, Chacon said.
Opposition lawmakers were not convinced by Chacon's answers.
In the past, other presidents have been caught taking gifts from private companies, but this was different and far more suspicious, said an opposition congressman, Gustavo Arias.
"It's the way she did everything, from not notifying Congress, to the question of why she had to use a private jet from an oil company and not pay for the trip herself", Arias added, noting that she was required to tell Congress about the trip.
Costa Rica has an Illicit Enrichment Law, which includes penalties of up to eight years in prison for public officials who accept gifts worth more than a minimum wage.
THX Energy, which declined to comment on the matter, is funded with Canadian capital according to its website.