(File image) United States President Barack Obama

Washington - The White House has investigated President Barack Obama’s advance staff for any link to a Secret Service sex scandal in Colombia but found no evidence of “improper” conduct, a spokesperson said on Monday.

The clearing of White House staff who had gone to Cartagena to prepare for President Barack Obama's arrival came as the Pentagon said it had suspended the security clearances of 11 military personnel over the incident in the resort.

A probe by the White House counsel's office “came to the conclusion that there is no indication that any member of the White House advance team engaged in any improper conduct or behaviour”, White House spokesperson Jay Carney said.

Carney added that the investigation was launched through “due diligence” - not from any suggestion that White House staff were involved with Secret Service agents who allegedly invited 20 prostitutes back to their hotel.

“There's been rumours published on the Internet by people with no editors and no conscience,” Carney said.

“But there is no specific allegation of any kind of misconduct here.”

Six Secret Service agents have lost their jobs over the incident, a total of 12 have been under investigation, along with 11 members of the military who were also in Colombia.

A defence official said on Monday that a member of the White House Communications Agency, which is staffed by military personnel, was also under investigation, bringing the total number of people being probed to 24.

Senate Homeland Security Committee Chairperson Joe Lieberman had called on Sunday for the White House to investigate whether any of its staffers were involved in the incident - a diplomatic embarrassment for Washington.

Defence Secretary Leon Panetta on Monday announced that the 11 members of the military implicated in the scandal which erupted earlier this month had had their security clearances revoked.

“We expect our people to abide by the highest standards of conduct,” Panetta told reporters on his plane en route to Colombia.

“We have suspended the security clearances of individuals there, pending the results of this investigation.

“Frankly, my biggest concern is the issue of security and what could have possibly been jeopardised by virtue of this kind of behaviour.”

Obama was briefed in person on the scandal for the first time by under-fire Secret Service Director Mark Sullivan on Friday.

The White House says it has confidence in Sullivan despite growing speculation he could be forced out over the embarrassing incident. Carney said the director did not offer his resignation to Obama on Friday.

The scandal over the events in Cartagena, ahead of Obama's arrival for the Summit of the Americas earlier this month, looks set to get more airtime this week as key congressional figures demand answers.

Congressman Peter King, chairperson of the House homeland security committee, sent Sullivan a letter with 50 detailed questions about the extent of the US Secret Service investigation and its operations.

Among his demands was a “comprehensive, minute-by-minute timeline of all known actions, locations and possible violations” of US or Colombian law, the Secret Service code of conduct and Homeland Security directives.

He also asked how many Secret Service agents paid money to prostitutes in Colombia and how many officers involved had sensitive material in their rooms, including details of Obama's schedule in Colombia.

The Cartagena incident first came to light after a dispute over payment involving one of the women led police to be called to the hotel and unleashed the biggest scandal in the presidential bodyguard's nearly 140-year history. - Sapa-AFP