The head of the US Marines has vowed to hold service members accountable for sharing nude photos of their female colleagues online.
Gen Robert Neller promised to change the Marine culture while testifying before a Senate committee.
Last week, reports emerged that current and former Marines were sharing photos on Facebook and on message boards, triggering a Navy investigation.
But female members of the Senate panel pushed back on Gen Neller's promises.
Senator Kirsten Gillibrand, a New York Democrat, said that the military had not done enough to address longstanding allegations of rampant sexual assault and harassment.
She pointed out that the Marines were rocked by similar allegations of online exploitation in 2013.
"When you say to us it's got to be different, that rings hollow," she said during the Senate Armed Services Committee on Tuesday.
"It is a serious problem when we have members of our military denigrating female Marines who will give their life for this country in the way they have with no response from leadership."
The pictures were posted within a members-only group called Marines United, and were accompanied by vulgar and highly aggressive sexual messages.
The group, which included around 30,000 active and retire male marines, has now been closed down.
Gen Neller, joined by acting Navy Secretary Sean Stackley, said the Naval Criminal Investigative Service (NCIS) was probing the scandal.
He also conceded the Facebook revelations may hinder female recruitment and that changes must be made within in Marine Corps culture.
"I'm the commandant. I own this, and we are going to have to, you know, you've heard it before, but we're going to have to change how we see ourselves and how we do, how we treat each other," Gen Neller told Senator Gillibrand.
"That's a lame answer, but ma'am that's the best I can tell you right now. We've got to change, and that's on me."
The Marine Corps has the lowest percentage of female members among the five military services. Women make up about 7 to 8% of all Marines.
Gen Neller said a "small number" of victims have come forward, but he repeated his appeal for more women to do so.
Mr Stackley said an NCIS tip line received more than 50 calls while officials are looking into more websites.
"This is a bell-ringer," Mr Stackley said. "We're not going to go backwards."
The Facebook group's activity was uncovered by The War Horse, a non-profit news organisation run by marine veteran Thomas Brennan.
Members encouraged each other to find and upload more images, according to The War Horse. They also identified the women by their names, ranks and units.
The photo sharing began in the same month that the first US Marine infantry unit began receiving women.
Both Gen Neller and Mr Stackley also addressed the legal challenges of prosecuting service members for online behaviour, which could be protected under privacy laws or free speech.
But lawmakers have suggested altering regulations to make so-called "revenge pornography" illegal under military code.
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