ISIS hackers have allegedly obtained and released personal information of up to 100 U.S. military personnel. The terror group has called on extremists in the U.S. to target those listed.

Calling itself the “Islamic State Hacking Division,” the alleged hackers posted online a list of 100 military personnel, with their names, addresses, photos and sometimes rank and called for their "brothers residing in America" to kill them, according to Reuters. The list was released on Saturday, and the Pentagon as well as the FBI are looking into its authenticity.

"I can't confirm the validity of the information, but we are looking into it," said a defense official, speaking on condition of anonymity.

Defense Department officials speaking with The New York Times refuted the claim that military servers were hacked, as the IS Hacking Division claimed. The officials said most of the information is available publicly and appears to have been gathered, in some cases, from public Pentagon reports on the campaign against ISIS.

Among those listed are some service members from a B-52 squadron based in North Dakota, hinting at the possibility the hackers are merely using public defense posts. A defense official said the squadron has not participated in the current operations while other photos shown originate from an official meeting with President Barack Obama.

"We always encourage our personnel to exercise appropriate OPSEC (operations security) and force protection procedures," an official told Reuters, saying the Pentagon is encouraging service members to secure their online presence.

On Twitter, the Pentagon’s news account, DoD News, tweeted a video about social media security and reminded troops of their online security.

Retired Gen. Carter Ham of U.S. Africa Command told ABC's "This Week" the news about the list are “very disconcerting” but added that the Pentagon in the last few years has continued to remind service members and their families to secure their online presence and “be very cautious about the information you put on social media."

“Disabling your geolocation, being very circumspect about the location of the service members for precisely the reason that has now played out,” he said.

Former Iraq War veteran and current Democratic congresswoman, Rep. Tulsi Gabbard of Hawaii, told CBS’s “Face the Nation” that groups like ISIS are using an unconventional approach in their war against the U.S. and those who do not follow their beliefs.

"These Islamic extremist terrorist elements are looking toward so-called 'soft targets,'" she said, adding there has been a rise in these tactics all over the world.