Washington - Two senior House of Representatives Republicans expressed confidence in the head of the US Secret Service on Sunday despite the agency's Colombia prostitution scandal while a Senate committee chairperson planned hearings into the matter.

Senator Joseph Lieberman, an independent, said that the Homeland Security and Governmental Affairs Committee that he chairs will send specific questions to the Secret Service this week about the scandal before the panel holds public hearings. Other congressional committees also are investigating.

The Secret Service, which protects the president, vice-president and other prominent US political figures, said on Friday that three more of its employees resigned. That brought to six the number who have departed in connection with alleged misconduct involving prostitutes in Colombia this month before President Barack Obama's trip to the seaside city of Cartagena.

The Secret Service also said a 12th employee had been implicated in the investigation into an incident that also involved 11 US military personnel.

Representative Peter King, chairperson of the House Homeland Security Committee, told the NBC programme Meet The Press that he expects several more Secret Service agents to leave the agency “within the very near future”.

At least 21 women were brought back to a beach front hotel and the behaviour of the Secret Service men was exposed when one of the Colombian women complained that she had not been paid enough, resulting in local police getting involved.

Lieberman also said the White House should launch its own internal review of all White House personnel and advance teams who were in Cartagena “to make sure that no one working for the White House was involved in any of the same kind of inappropriate behaviour that the Secret Service agents were”.

Secret Service Director Mark Sullivan was given an endorsement on Sunday by King and a second Republican House committee chairman.

“Director Sullivan, from the moment this broke, has moved effectively and this investigation is going full speed ahead,” King said. “I believe Director Sullivan has done a fine job.”

King added that procedures must be put in place “to ensure it never happens again.”

Representative Darrell Issa, chairperson of the House Oversight and Government Reform Committee, told Meet The Press that he has “great confidence” in Sullivan's handling of the investigation into the matter.

Asked whether he has confidence in Sullivan, Lieberman said: “I do at this point... I think he's conducting a comprehensive investigation.”

Lieberman said his committee's investigation will seek to determine whether the actions in Colombia were part of a pattern of behaviour that happened over time elsewhere and what steps will be implemented to prevent any such actions in the future.

“It's more serious than just a frolic. History is full of cases where enemies have compromised people and security or intelligence of positions with sex,” Lieberman said on the programme Fox News Sunday.

He told the CBS programme Face The Nation: “For Secret Service agents who have the responsibility to protect the president, to act as these people did in Cartagena, as if they were college kids on a spring break, is reprehensible.”

King's office released a letter he sent to Sullivan, dated Friday, asking for answers to 50 questions about the matter, including whether any White House officials were involved in the incident in Cartagena.

David Axelrod, senior advisor to Obama's re-election campaign, said the president has confidence in Sullivan and the Secret Service. “But this is really disturbing. We have to get to the bottom of it and I'm sure that we will,” he told NBC's Meet The Press. - Reuters