The U.S. Secret Service says three of 11 employees under investigation for alleged misconduct involving prostitutes in Colombia are leaving the agency.

The agency's assistant director, Paul Morrissey, says the three leaving include one “supervisory” employee. He said the investigation into the scandal is still in an early stage.

Eleven Secret Service personnel who were stationed in Colombia ahead of U.S. President Barack Obama's arrival for the sixth Summit of the Americas were sent home and placed on administrative leave pending an investigation. Pentagon officials have said at least nine military members also may have been involved in the alleged misconduct.

The ranking Republican on the Senate's Homeland Security and Governmental Affairs Committee, Senator Susan Collins, says at least 20 foreign women were brought to the hotel in Colombia where alleged misconduct occurred involving Secret Service members, military staff and prostitutes before the president's visit.

U.S. chairman of the Joint Chiefs of Staff, General Martin Dempsey, said earlier this week that he was “embarrassed” by the alleged scandal. He said the military arm “let the boss down” by causing a distraction to an important regional engagement for the president.

The Secret Service has said none of the personnel involved was assigned to protect Mr. Obama.