SAN JOSE Costa Rica's attorney general's office has opened an investigation into the disappearance of some $6 million at the Central American country's largest commercial bank, bank officials said on Tuesday.

The 3.3 billion colones ($6.2 million) in question were first detected missing at the National Bank of Costa Rica in August through internal audits, and five employees have been suspended as a result, the bank's interim manager, Jaime Murillo, told a press conference.

The attorney general's office is investigating five officials, including an accountant, supervisors and a guard.

"We cannot say for sure that this is fraud or that someone stole this cash. We are not at that point yet. It is under investigation," Murillo said, adding that such a situation had never before occurred in the bank's 109-year history.

The bank's clients are not at risk, the official added.

The bank reported that it does not know when or how the money went missing, adding that the details will be clearer after the attorney general's office's investigation and an internal investigation by the bank.

($1 = 530.1500 colones)

(Reporting by Alvaro Murillo; Writing by Brendan O'Boyle; Editing by Sandra Maler)