FBI agents have identified a dozen cases of possible "insider threats" among Islamic extremists within American military ranks, National Public Radio reported Monday. That includes active duty troops, reservists and civilians with access to military facilities.

The figure was drawn from more than 100 investigations and was reported to members of a House-Senate committee meeting secretly in December. Officials declined to say whether any additional cases have been identified since then.

During a hearing last Wednesday on extremism within the Muslim community, House Homeland Security Committee Chairman Peter King, R-N.Y., said military communities increasingly are targeted for attacks in the United States.

"The number of military insiders suspected of being radicalized to violent Islamist extremism is a still-classified but truly eye-popping amount of ongoing cases," King said in prepared remarks.

Last month, Army Pvt. Naser Jason Abdo was convicted of attempting to use a weapon of mass destruction and attempted murder in connection with his plan to blow up a restaurant popular with Fort Hood personnel last summer. He planned to shoot survivors who then tried to escape.

He told his mother that he had a religious obligation to act in response to American military action in Afghanistan and Iraq.

Two years earlier, Fort Hood was the site of the deadliest terrorist attack on American soil since 9/11. Army psychiatrist Nidal Hasan opened fire at a base processing center, killing 13 people and wounding 32 others. During his service before the attack, Hasan told colleagues that the United States was at war with Islam, justified suicide bombing and said his religious loyalties outweighed his oath to protect America.

The cases identified as posing serious threats include people who may be plotting attacks or who may be communicating with "dangerous individuals" who encourage the subject to attack.