A former Iraqi translator for the U.S. military was arrested on May 14 in Texas and charged with lying about his support for the leader of the Islamic State.
Bilal Abood, 37, lied to FBI agents about posting an oath on Twitter to Abu Bakr al-Baghdadi, the leader of the militant Muslim group, according to a criminal complaint.
A search of Abood's computer found he was watching IS beheadings and in 2013 traveled to Syria where the group had declared a caliphate.
Abood, who immigrated to the United States in 2009 and became a naturalized citizen, is in federal custody pending a detention hearing in Dallas May 15.
His attorney could not be reached for comment.
Lying to federal agents is punishable by up to eight years in prison and a fine of up to $250,000.
U.S. authorities have vowed to move quickly against people suspected of engaging with the Islamic State to deter others from becoming involved with the group.