A U.S. Army sergeant described by former colleagues as a one-time "model soldier" is due to be sentenced in a Hawaii federal court on Tuesday after pleading guilty to providing material support to the Islamic State militant group.

Ikaika Erik Kang, 35, agreed to a plea deal in August on four counts of breaking anti-terrorism laws in which he accepted a proposed sentence of 25 years in prison.

Kang had begun expressing support for Islamic State, designated by the United States as a foreign terrorist organization, by early 2016, according to the U.S. Department of Justice.