Defence Secretary James Mattis said “all appropriate action” was being taken in all branches of the armed forces.
The scandal began when nude photos of female Marines were published online by male colleagues.
But fewer than 10 female Marines have come forward to make a formal complaint, a top Marine official said.
The scandal initially broke when current and former members of the US Marines were discovered sharing naked photos of female servicewomen on Facebook, in a group called “Marines United”.
Since then, it has emerged that other anonymous online message boards have been soliciting and publishing hundreds of nude photos of female personnel from other armed forces.
“If you’re participating in this type of behaviour in any way shape or form – you’re not helping me or your Marine Corps,” he said.
“You know we claim that being a Marine is a special title and something that you earn. There’s honour here. But there is no honour in denigrating a fellow Marine in any way shape or form.”
One online message board seen by the BBC – which remains publicly accessible – indicates that such practices extend throughout the military.
Often, such posts included names and personal details of the women, including where they were stationed.
“Just heard [name redacted] and her bf [name redacted] broke up,” reads a comment on 19 December from an anonymous user on a post that appears to involve personnel at Offutt Air Force Base in Nebraska.
“Maybe he would post some.”
Another post from a different anonymous user on 12 September reads: “Any wright patt wins? I’ll start off with some.” The post refers to Wright-Patterson Air Force Base in Ohio.
The user then posts self-taken images of a woman in a bikini, and then topless. There are many more explicit images on the message board.
On Wednesday, two women who said they were victims spoke out publicly alongside their lawyer, urging others to come forward.
“I can tell you that this exact behaviour leads to the normalisation of sexual harassment and even sexual violence,” said Erika Butner, 23, who served in the Marines for four years until last June.
The Senate Armed Services Committee is due to hold a hearing on the issue next week.
Marines United’s activity was first uncovered by The War Horse, a non-profit news organisation run by Marine veteran Thomas Brennan.
Some of the photos are believed to have been taken surreptitiously. Other images are thought to have been consensual, but posted without permission.
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