US naval investigators are probing allegations that Marines distributed nude pictures of female service personnel without their consent, officials said Monday.
The explicit photos, shared on a secret Facebook page which has since been taken down, reportedly showed female Marines and other women in various states of undress.
Posts on the website, called "Marines United," also contained lewd comments about some of the women.
The story was first reported by The Warhorse, a news group run by Marine veteran Thomas Brennan.
He said some of the photos were taken surreptitiously, while others had been taken by the women themselves but shared without their consent.
"The Marine Corps is deeply concerned about allegations regarding the derogatory online comments and sharing of salacious photographs in Marines United, a closed website," the United States Marine Corps (USMC) said in a statement on its website.
"This behavior destroys morale, erodes trust and degrades the individual. The Marine Corps does not condone this sort of behavior, which undermines its core values."
Because the Marine Corps is part of the Department of the Navy, the scandal is being investigated by the Naval Criminal Investigative Service.
"NCIS is investigating those who are posting explicit photos without the permission of the person in the photos, which is potentially a felony. Beyond that, NCIS does not discuss the details of ongoing investigations," the agency said in a statement.
Pentagon spokesman Navy Captain Jeff Davis said Defense Secretary Jim Mattis, himself a retired four-star Marine, found the allegations "troubling."
"He's communicated with the commandant of the Marine Corps, General (Robert) Neller, and has indicated that he trusts the Marine Corps will take all steps to maintain good order and discipline," Davis said.
Fox News reported that those with access to the site included active-duty and retired male Marines, Navy personnel and British Royal Marines.
The head of the US congressional committee that oversees the military called the website "unacceptable."
"Revelations of this sort of treatment against fellow Marines are troubling," said Mac Thornberry, chairman of the House Armed Services Committee.
"Degrading behavior of this kind is entirely unacceptable. They and the nation deserve better.
"I expect the Marine Corps to investigate this matter fully with appropriate consequences for those who willingly participated."