WASHINGTON  - Three more US Secret Service agents quit over a widening scandal in Colombia, as President Barack Obama got his first briefing on the notorious incident from the agency’s director.

The new resignations bring to six the number of agents who have lost their jobs over claims that they brought prostitutes back to their hotel in the Caribbean resort of Cartagena, host of last weekend’s Summit of the Americas.

A twelfth member of the elite protection agency has now been implicated in the incident, a deep diplomatic embarrassment for the United States that overshadowed Obama’s visit to Colombia. The Secret Service said in a statement announcing the resignations that one employee had been cleared of misconduct, but would face administrative action.

“The Secret Service continues to conduct a full, thorough and fair investigation, utilizing all investigative techniques available to our agency,” the statement said. Including military officers, who were also in Cartagena to protect the president, there are now 23 Americans under investigation over the late night-spree of drinking and alleged inappropriate behavior.

The agency, known for its sharp-suited agents with earpieces ready to take a bullet for the US president, is using polygraph lie detector techniques in the probe. Obama has said he will be “angry” if details of the scandal aired in the press are true. He got his first briefing on the incident from Secret Service Director Mark Sullivan on Friday afternoon in the Oval Office, a senior US official said.

There have been mounting suggestions in Washington that Sullivan could lose his job over the scandal, reportedly involving 20 prostitutes, but the White House said Obama retains confidence in him.

But officials also say they will not comment further on the sleazy goings on in Cartagena until the results of an investigation are released. The US military earlier said it was now investigating 11 service members linked to events in Colombia. Six suspects were from the US Army’s 7th Special Forces Group, two from the Marine Corps, two from the Navy and one from the Air Force, said a spokesman for US Southern Command, which oversees forces in Central and South America.

An Air Force colonel in charge of the investigation flew to Colombia on Monday to gather facts in the case and was due return to the United States probably over the weekend.

He then will interview the suspects.

Former Republican vice presidential nominee Sarah Palin was meanwhile dragged into the controversy over a Facebook posting reportedly made by one of the three agents who lost their jobs on the agency on Wednesday.

Agent supervisor David Chaney reportedly added a caption to a Facebook picture showing him protecting the former Alaska governor in 2008, reading that he was “checking her out.”

“Well, check this out bodyguard, you’re fired,” Palin said on Fox News on Thursday, before going on to argue that the scandal was a symptom of administrative failings in Obama’s government.

“The president, the CEO of this operation called our federal government, has got to start cracking down on these agencies,” Palin said.

White House spokesman Jay Carney objected to Palin’s comments, and similar ones by Republican Senator Jeff Sessions, calling them “preposterous” and “ridiculous” and said the Secret Service should not be politicized.

The Washington Post on Thursday named another agent who resigned in the first batch of departures as Greg Stokes, a member of the Secret Service’s K-9 division. Another agent was Wednesday told he would be fired.

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.

The New York Times on Wednesday published comments from the 24-year-old single mother at the center of the hoopla, saying a Secret Service agent had reneged on a deal to pay her $800 for the night and ended up paying only $30.

But in Cartagena, bouncers at the door of the night club concerned expressed as much shock as most Americans about the furor.

“You are wasting your time. The Pley Club is not the place where the security agents went,” one of them told AFP.

But widespread reports, first divulged by ABC, said the agents did go the brothel, drinking expensive liquor and bragging about working for Obama.