Ikaika Kang, 34, a soldier in the 25th Combat Aviation Brigade, 25th Infantry Division, in Hawaii had been under investigation by the Army and FBI for more than a year and was taken into custody on July 8, the FBI said.
According to a criminal complaint filed in U.S. District Court in Honolulu, Kang has sworn allegiance to IS, the militant group that seized large swaths of territory in Syria and Iraq for a self-proclaimed caliphate in 2014.
He also is accused of attempting to provide military documents and training to the group, the FBI said.
U.S. authorities said they believe that Kang was a "lone actor" who had no known associations with anyone who might pose a threat to the United States.
Kang enlisted in the army in December 2001 just months after the September 11 attacks. He served in Iraq from March 2010 to February 2011 and Afghanistan from July 2013 to April 2014.
Based on reporting by AP and Reuters
Comment: Kang was only following the same course set by the US. His mistake was in thinking a low level soldier could engage in the same deplorable behavior as high ranking politicians like Hillary Clinton.