A U.S. lawmaker on the Senate's Homeland Security and Governmental Affairs committee says at least 20 foreign women were brought to the hotel in Columbia where alleged misconduct occurred involving Secret Service members, military staff and prostitutes.

Republican Senator Susan Collins made the announcement Tuesday after Secret Service director Mark Sullivan briefed her on the situation.

Senator Joe Lieberman, the chairman of the Senate's Homeland Security committee, told reporters Tuesday that “compromising positions off-duty” can “create a risk to national security.” He says those who opened themselves to that risk should be “punished severely.”

Pentagon officials have said at least nine military members may have been involved in the alleged misconduct.

The U.S. chairman of the Joint Chiefs of Staff, General Martin Dempsey, said in a press conference at the Pentagon Monday 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.

U.S. Defense Secretary Leon Panetta added that it is a “requirement” for our forces to abide by the “highest standard.” He said that if found in violation, the people involved in the scandal will be held accountable.

Eleven Secret Service personnel who were stationed in Colombia ahead of President Barack Obama's visit were sent home and placed on administrative leave pending an investigation that involved prostitution. At least five U.S. military staff assigned to support the Secret Service were confined to their barracks in Colombia after the allegations.

The alleged misconduct reportedly took place before President Barack Obama arrived in the resort city of Cartagena Friday for the sixth Summit of the Americas.

The White House said Tuesday Mr. Obama has confidence in the Secret Service director and believes he responded swiftly to the incident.

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