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The White House says it has found no evidence its advance staff were implicated in the Secret Service sex scandal in Colombia.

Spokesman Jay Carney said there was "no indication of misconduct", but revealed that an internal investigation had been launched by White House lawyers.

Meanwhile, a 12th military service member has been linked to the scandal.

One member of Congress says he expects more Secret Service agents to be forced out in the coming days.

Six agents have already resigned or been forced out.

Mr Carney said the White House investigation had been launched on Friday out of "due diligence".

Reports say a disagreement between an agent and a prostitute sparked a row, blowing the lid off a night that saw 20 women taken back to a hotel in the Caribbean port city of Cartagena.

None of the individuals involved were part of President Barack Obama's personal security detail, but were in the city in advance of his trip to the Summit of Americas.

New York Congressman Peter King, chairman of the House Â鶹ԼÅÄland Security committee, told NBC News "countless agents" were still interviewing women involved in the scandal, as well as Secret Service employees.

"I think we expect in the next day or so to see several more agents being forced to leave," Mr King said.

Congress will also widen its investigation into the agency, according to Mr King's counterpart in the Senate, Joe Lieberman.

Mr Lieberman said his committee wants to determine whether the scandal in Colombia was part of "a pattern of misconduct that has gone on elsewhere by Secret Service agents".