White House defends Secret Service amid prostitution investigation April 17, 2012 -- Updated 2133 GMT (0533 HKT) White House Press Secretary Jay Carney said President Obama has confidence in his CIA director. White House says Obama has confidence in Secret Service chief A Republican senator says as many as 21 prostitutes may have been involved The allegations overshadowed Obama's visit to a pan-American summit in Colombia Washington (CNN) -- The White House defended the Secret Service and its director Tuesday amid an embarrassing investigation into whether several agents brought prostitutes back to their hotel in Colombia ahead of a presidential visit. Eleven Secret Service members and as many as 10 U.S. military personnel assisting them have been implicated in the investigation, which began Thursday after one of the women complained that she hadn't been paid. The Americans were in Cartagena to prepare for President Barack Obama's weekend visit to the Summit of the Americas, and Obama has said he expects a "rigorous" investigation. The investigation is being led by Secret Service Director Mark Sullivan, who has been briefing members of Congress. A leading senator said Tuesday she had been told as many as 21 women had been involved, and questioned whether the incident could have endangered the president. Who were these women? Could they have been members of groups hostile to the United States? Could they have planted bugs, disabled weapons, or in any other [ways] jeopardized security of the president or our country?" said Maine's Susan Collins, the ranking Republican on the Senate Homeland Security Committee. At the White House, presidential spokesman Jay Carney said Obama "has confidence" in Sullivan, who he said "acted quickly in response to this incident," and in the agents around him. "The work the Secret Service does, the men and women who protect him and his family and those who work with him, is exemplary as a rule," Carney said. They put their lives on the line, and it is a very difficult job, and he acknowledges that and he appreciates it. Collins said she believed Sullivan "will fully investigate" the allegations and take "appropriate action" if the allegations bear out. But she questioned whether there was any similar misconduct on previous missions, and whether the issue is a sign of a deeper problem within the agency. The Secret Service agents and officers involved range in experience from relative newcomers to nearly 20-year veterans, and all have been interviewed at least once, two government officials with knowledge of the investigation told CNN on Monday. U.S. government sources have said there was a dispute between at least one Secret Service member and a woman demanding payment. The alleged misconduct occurred before Obama arrived in Cartagena, and the Secret Service said the personnel involved were relieved of duty and sent home before the president landed. But the news broke while he was there -- and Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, told reporters at the Pentagon on Monday that the incident distracted attention "from what was a very important regional engagement for our president."