(AP) — A top lawmaker briefed on the investigation into a Secret Service prostitution scandal said more firings could be imminent following the ouster of three agency employees.

“I wouldn’t be surprised if you saw more dismissals and more being forced out sooner rather than later,” Rep. Peter King, R-N.Y., said Thursday. King is being updated on the investigation by Secret Service Director Mark Sullivan.

“You may see a few more today or tomorrow,” King added.

The Secret Service has moved quickly to quell the scandal that erupted late last week, when at least some of 11 agency employees implicated in the incident brought prostitutes back to their hotel in Cartagena, Colombia, where they were setting up security for a visit by President Barack Obama.

So far, three people involved have lost their jobs. The service said Wednesday that one supervisor was allowed to retire, and another will be fired for cause. A third employee, who was not a supervisor, has resigned.

In Washington and Colombia, separate U.S. government investigations are under way. The Secret Service has investigators in Colombia, and King said he has assigned four congressional investigators to the probe. The House Committee on Oversight and Government Reform, led by Rep. Darrell Issa, R-Calif., sought details of the Secret Service investigation, including the disciplinary histories of the agents involved.

In a letter to the Secret Service director, Issa and Rep. Elijah Cummings of Maryland, the committee’s senior Democrat, said the agents “brought foreign nationals in contact with sensitive security information.” The lawmakers have demanded that Sullivan provide them by May 1 with detailed information about the incident, including a full timeline of the events that unfolded in Colombia and assurances that none of the women involved were under the age of 18.

Senate Majority Leader Harry Reid called the Secret Service employees under investigation “stupid” and said there is not much Congress can do to stop others from making similar choices.

“There is not a bill we can pass to cause people to have common sense,” Reid, D-Nev., said Thursday.

Issa said Thursday he would wait until the Secret Service finished its internal investigation before deciding whether to launch his own committee probe.

While congressional lawmakers pushed for more answers from the Secret Service, the White House, frustrated by the election-year embarrassment, pleaded for patience.

“What I’m not prepared to do is to offer you sort of day-by-day commentary on new revelations or even new actions taken with regards to this investigation while it’s still under way,” White House spokesman Jay Carney said. “I don’t think that’s helpful to the process.”

Carney said Obama remained confident in the Secret Service chief, though he said the president had not talked with Sullivan since the incident unfolded. Senior White House aides were in touch with Sullivan about the ongoing investigation.

One Republican lawmaker said Thursday the Secret Service incident raised questions about whether Obama was capably leading the government.

“I don’t sense that this president has shown that kind of managerial leadership,” Sen. Jeff Sessions, R-Ala., said.

Carney shot back: “That sounds very much like a lawmaker attempting to politicise something that is not at all political.”

Hours after launching his criticism of the president, Sessions showed up at the White House to attend a ceremony honouring his home-state University of Alabama football team.

The Secret Service employees under investigation include members of the agency’s “jump teams,” which are sent to sites ahead of the president’s arrival to set up security. Others involved are on counter-assault and counter-sniper teams. The majority of those involved are believed to be based in the Washington area.

Two of the employees forced out Wednesday were supervisors in the agency’s uniformed division; one is a sergeant, according to a person familiar with Secret Service operations and refused to be identified because he was not authorised to discuss the matter.

Eight other Secret Service employees remain on administrative leave and have had their top-secret clearance revoked.

Sullivan has offered the agents under investigation the opportunity to take a polygraph test, though the agents can refuse.

The scandal also involved about 10 military service members and as many as 20 women.

King said agency investigators in Colombia still have not been able to talk to the women who were brought back to the hotel. The investigators do, however, have the names, addresses and pictures of the women, said King, the chairman of the House Homeland Security Committee, which oversees the Secret Service.

The lawmaker said the agency was “reasonably confident” that drug use was not an issue with the three agents who have been forced out. But he said Secret Service investigators would continue to look into whether drugs played a role in the incident as they talk to the other eight agents involved.

The episode took a sharp political turn Wednesday when presumptive Republican presidential nominee Mitt Romney said he would “clean house” and fire the agents involved. However, Romney said he, too, continued to have confidence in Sullivan.

The 10 military personnel under investigation were staying at the same hotel at the service employees. The troops are suspected of violating curfews set by their commanders.

Two U.S. military officials have said they include five Army Green Berets. One of the officials said the group also includes two Navy Explosive Ordinance Disposal technicians, two Marine dog handlers and an Air Force airman. The officials spoke on condition of anonymity because the investigation is still under way.

Sullivan, who this week has briefed lawmakers behind closed doors, said he has referred to the case to an independent government investigator.