WASHINGTON (Reuters) - US Senators grilled the Navy and the Marine Corps' top leaders on Tuesday (March 14) amid a growing scandal involving a private Facebook group and its surreptitious distribution of explicit images of women in the armed forces - often with obscene, misogynist commentary.

The Facebook group, called "Marines United," is reported to have nearly 30,000 followers, including active-duty US Marines, Marine Corps veterans and British Royal Marines.

"If we can't crack Facebook, how are we supposed to be able to confront Russian aggression and cyber hacking throughout our military?" Democratic Senator Kirsten Gillibrand asked during a Senate Armed Services Committee Hearing.

Ms Gillibrand said online harassment had become evident as early as 2013 and military leaders were made aware of it but have still been unable to stop.

"I don't have a good answer for you," the Commandant of the Marine Corps General Robert Neller said. "We've got to change, and that's on me."

Mr Neller has vowed to hold those responsible for the photo sharing accountable and change the culture behind it.

Republican Senator Lindsey Graham said that the scandal could have an impact on recruiting women, and called it"devastatingly bad." The Naval Criminal Investigative Service (NCIS) has opened an inquiry into the matter.

Acting Navy Secretary Sean Stackley said more than 50 calls had been received on an NCIS tip line so far and that the scandal could involve more websites.

US Defense Secretary Jim Mattis said in a statement last week that personnel involved in any alleged sharing of nude photos of female colleagues were guilty of "egregious violations of the fundamental values."

The US Code of Military Justice explicitly outlaws distribution of sexually explicit photos of others without their consent as an offense punishable by court-martial.