By Phil Stewart
BOGOTA, April 23 (Reuters) - A 12th U.S. military service member was linked to a prostitution scandal in Colombia on Monday and the Pentagon suspended the security clearance of personnel implicated in the events ahead of President Barack Obama's visit earlier this month.
Twelve Secret Service employees have also been implicated in the incident, the worst scandal in decades for the agency responsible for the safety of the president and other senior officials. Six of those have since left the Secret Service.
The 12th military service member, attached to the White House Communications Agency, has been relieved of his duties pending the outcome of an investigation, according to a U.S. defense official, who spoke on condition of anonymity.
U.S. Secret Service and military personnel allegedly took as many as 21 women back to their beachfront hotel in Cartagena on the night of April 11-12, just before Obama arrived in the seaside city to attend the Summit of the Americas.
They were discovered when one woman complained about money, leading to the involvement of the local police.
"We expect our people, wherever they are, whether they are in Colombia or any other country ... to behave at the highest standards of conduct," U.S. Defense Secretary Leon Panetta told reporters at Colombia's Tolemaida military base.
"If these investigators find that there have been violations ... those individuals will be held accountable."
Panetta said the Pentagon had suspended security clearance for the military personnel implicated in the scandal, although it was unclear how many of the 12 individuals had such clearance.
"Frankly, my biggest concern is the issue of security and what could possibly have been jeopardized by virtue of this kind of behavior," Panetta said.
The incident embarrassed the United States and overshadowed Obama's participation at the summit.
Hiring prostitutes, no matter the legal status where the act takes place, is prohibited for U.S. military personnel. Those convicted under the military justice system can be imprisoned for up to a year and be discharged dishonorably.
Meanwhile, the conduct of the White House staff and advance team for Obama's Colombia visit had been reviewed and cleared, White House spokesman Jay Carney said on Monday.
Independent U.S. Senator Joseph Lieberman had said on Sunday that the White House should launch an internal review of all White House personnel and advance teams who were in Cartagena.
During his trip to Colombia, Panetta announced that the United States would facilitate the sale of 10 helicopters to its South American ally, including five U.S. Army Blackhawks that have been in service in Afghanistan. The other five are commercial helicopters.
Panetta said the United States would continue to provide training, equipment and assistance that Colombia has requested to defeat the Revolutionary Armed Forces of Colombia, or FARC, who he termed a common enemy.
"The United States stands in solidarity with Colombia and its campaign against the FARC," he said of Colombia's largest guerrilla group.
A U.S. official called the Blackhawks a "scarce commodity."
Helped by billions of dollars in U.S. aid in the last decade, Colombia's armed forces have used better intelligence and mobility to batter guerrilla armies, pushing their fighters into ever more remote hideouts.
The FARC has adjusted its tactics, however, by returning to its guerrilla roots and using smaller units - in contrast to the 1990s when it seized large swathes of territory. (Editing by Doina Chiacu and David Brunnstrom)