Updated 8:03 PM ET
(CBS/AP) CBS News has learned through a law enforcement source that three more Secret Service agents have resigned in the wake of the Colombia prostitution scandal.
In addition, CBS News investigative producer Pat Milton reported that one other employee of the Secret Service has been implicated and is now under investigation, bringing the total of agents to 12. That agent has been placed on administrative leave. One of the agents previously under investigation has been cleared of serious wrongdoing but will face administrative action.
The service of the agents range from three to 12 years with the Secret Service.
Rep. Peter King, chairman of Homeland Security, told CBS News that 12th agent added was from a separate incident that happened five days before the Hotel Caribe night. The agent went out on the town and was staying at Hilton. Whatever he did, and King does not know, it was considered improper conduct. This information was found because investigators in Cartagena are interviewing employees at every hotel secret service stayed.
Also late Friday, Republican Sen. Chuck Grassley of Iowa urged a broader investigation, including checking hotel records for White House advance staff and communications personnel who were in Cartagena for the summit. In a letter to Sullivan and the inspector general at the Homeland Security Department, Grassley asked whether hotel records for the White House staffers had been pulled as part of the investigations.
Friday's developments would make six Secret Service employees forced out of the agency. Two supervisors and another employee were forced out earlier this week.
The agency released a statement that read: "At this point, five employees continue to be on administrative leave and their security clearances remain suspended pending the outcome of this investigation."
CBS News correspondent Norah O'Donnell reported that President Obama called in Secret Service director Mark Sullivan into the Oval Office for a face-to-face briefing on the investigation Friday afternoon.
As previously reported, the U.S. military said 11 service members are being investigated for alleged misconduct in Colombia. That's up from the 10 personnel the military last believed to be involved.
The military says six are from the Army, two each are from the Marines and Navy and one is from the Air Force. The Marine and Navy personnel are from San Diego and the Air Force member is from Charleston, S.C. The Army personnel are from the 7th Special Forces Group.
The military says the service members have returned to their commands. It says they have not been charged and are not under detention.
The service members were staying in the same Colombian hotel as 11 Secret Service employees who are under investigation for alleged misconduct involving prostitutes.
Eleven Secret Service employees were put on administrative leave last week following an incident in Colombia that involved at least some agency personnel bringing prostitutes to their hotel room. The scandal, which involves as many as 20 Colombian women, broke last week after a fight over payment between a prostitute and a Secret Service agent spilled into the hotel hallway. A 24-year-old Colombian prostitute told The New York Times that the agent agreed to pay her $800 for a night of sex but the next morning offered her only $30. She eventually left the hotel, she told the newspaper, after she was paid $225.
The scandal involved 11 officers and supervisors and at least 11 military members who were working on security before President Barack Obama arrived in Cartagena, Colombia, for the Summit of the Americas last week. The Pentagon acknowledged Friday that an 11th military person, a member of the Army, was implicated in the scandal.
Sources tell CBS News Secret Service officials believe their personnel picked up women at four different locations in Cartagena.
The Secret Service briefed about two-dozen congressional staff members Friday, mainly from the Senate Judiciary Committee, according to one individual who was there but was not authorized to be quoted by name.
The person said investigators have photo ID's and names from a Cartagena, Colombia, hotel registry for all the women who stayed overnight and are in the process of conducting interviews. Investigators have interviewed maids and said no alcohol or drugs were found in the rooms.
Those under investigation were offered polygraphs and drug tests. It is unclear whether anyone accepted, the person said.
As for the military personnel involved, Pentagon press secretary George Little said Defense Secretary Leon Panetta was getting regular updates on the investigation.
"He understands the level of interest in this issue," Little said. "He has serious concerns about the alleged misconduct."
Little said members of Congress have not yet been briefed on the military investigation but would be "in the near future."
In a letter to Secret Service employees Monday and obtained by the AP, Director Sullivan said the agency had moved in a "swift, decisive manner immediately after this incident was brought to our attention." He praised "the overwhelming majority" of employees who he said had acted with the "highest levels of professionalism and ethical behavior."
"Our job, our mission, our responsibility is to the president, the American people and the individuals we are entrusted to protect," Sullivan said. "This is not just a matter of honor, although this is critical. It is imperative, as part of our sworn duties, to always act both personally and professionally in a manner that recognizes the seriousness and consequence of our mission."
The lawyer for ousted Secret Service supervisors David Chaney and Greg Stokes, Lawrence Berger of New York, said Friday that Obama's safety was never at risk and said leaks surrounding the ongoing investigations "distort the process."
Regardless of what happened inside hotel rooms, Berger said, it never jeopardized the president's security. Berger said he could not comment on the woman's claims about being paid for sex, but added, "I don't think anything she has said is material to any of the issues I am pressing with my clients."
"Nothing that has been reported in the press in any way negatively or adversely impacted the mission of that agency or the safety of the president of the United States," Berger said.
Chaney and Stokes were forced out of the agency Wednesday. A third agent, who has not been identified and was not a supervisor, resigned.
On Chaney's Facebook account, which was made inaccessible on Friday, Chaney joked that he was checking out former Republican vice presidential candidate Sarah Palin while he was protecting her in 2008. The AP published a photograph it took of Chaney working in Palin's protective detail in October 2008 during a campaign rally in Carson, Calif.
"I was really checking her out, if you know what i (sic) mean?" Chaney wrote after a friend commented on the picture posted in January 2009 on Chaney's Facebook account.
Speaking on Fox News late Thursday, Palin said the joke was on Chaney.
"Well check this out, buddy -- you're fired!" Palin said.
All the 11 Secret Service employees have had their top-secret security clearances lifted.
The Secret Service investigation has included interviews of agents and hotel staff. CBS News has learned the investigators have now spoken to a number of the women. King does not know specifically what they've found from women yet.
The tawdry affair has also prompted a military investigation of 11 service members, including six members of the Army, two Navy Explosive Ordinance Disposal technicians, two Marine dog handlers and an Air Force airman.
An Air Force colonel and a military lawyer were also dispatched to Colombia this week. Under the Uniform Code of Military Justice, patronizing prostitutes is a crime for military personnel. It is referred to as "compelling, inducing, enticing or procuring a person to have sex in exchange for money; or receiving money for arranged sex." The UCMJ applies regardless of whether the service member is in the U.S. or abroad.
Officials from U.S. Southern Command, which organized the military role for the security operation, have not provided details of its probe beyond saying that at least some of the military members violated curfew and may have been involved in "inappropriate conduct."
White House press secretary Jay Carney said it was "preposterous to politicize" the issue, responding to criticism from Alabama Sen. Jeff Sessions and Palin, who have said the allegations reflect poor management of the government under Obama.
Palin described the affair Thursday as a "symptom of government run amok."
"It's like, who's minding the store around here?" Palin told Fox.