US Defense Minister Jim Mattis denounced the practice as "egregious violations of the fundamental values we uphold at the Defense Department."
"The chain of command is taking all appropriate action to investigate potential misconduct and to maintain good order and discipline throughout our armed forces," the retired Marine general said in a statement.
The scandal broke over the weekend with the revelation that pictures of female Marines in various stages of undress had been shared on a secret Facebook group called "Marines United."
Membership in the group was restricted to current and former Marines, but it had as many as 30,000 members before it was taken down.
The story was first reported by The War Horse, 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.
That was followed by a report Thursday that hundreds of pictures of naked women from all the military services were being shared on another image-sharing site, AnonIB.
Business Insider, an online news site, said the message board was threaded with conversations among men, many of whom asked for naked photographs of specific women, often identifying them by name and where they were stationed.
Probes have been ordered into the case, but Pentagon spokesman Jeff Davis appealed to members of the military to cooperate with investigators.
"Our values extend on and off duty and we want personnel experiencing or witnessing online misconduct to promptly report matters to their chain of command," he said.
He said if they weren't comfortable reporting to their military superiors, they could go to family support services, equal opportunity offices, sexual harassment prevention teams, the Pentagon's inspector general's office or law enforcement.
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