HONOLULU — An active duty U.S. soldier was arrested on terrorism charges after authorities say he pledged allegiance to the Islamic State group and said he wanted to “kill a bunch of people.”

The FBI arrested Sgt. 1st Class Ikaika Kang, 34, in a suburb of Honolulu over the weekend after a yearlong investigation involving multiple undercover officers and confidential informants. He made an initial appearance in federal court on Monday.

Kang’s court-appointed defense attorney, Birney Bervar, said it appears his client may suffer from service-related mental health issues of which the government was aware but neglected to treat. Bervar declined to elaborate.

He said Kang was “a decorated veteran of two deployments” to Iraq and Afghanistan.

A 26-page affidavit from FBI Special Agent Jimmy Chen filed in court Monday detailed how Kang thought he was dealing with people working for Islamic State but who were actually undercover agents.

Paul Delacourt, the FBI special agent in charge of the Hawaii bureau, said Kang gave military documents to people he believed would give them to Islamic State, but none of them got to the organization. He told reporters the FBI believed Kang was a lone actor and wasn’t affiliated with anyone who poses a threat.

On Saturday, agents arrested him after he pledged loyalty to an Islamic State leader and said he wanted to “kill ‘a bunch of people.’”