The U.S. Secret Service says three more employees have resigned over a scandal in Colombia involving prostitutes, and says President Barack Obama has been briefed on the matter by the agency's director.

The Secret Service said Friday the new resignations bring to six the number of agents who have lost their jobs because of the scandal. They also said that a 12th member of the protection agency has been implicated in the matter.

U.S. officials say Secret Service Director Mark Sullivan came to the White House late Friday to personally brief President Obama.

The Secret Service personnel were stationed in Colombia ahead of U.S. President Barack Obama's arrival for the sixth Summit of the Americas. Pentagon officials have said at least 10 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.