A 19-year-old Minneapolis man charged with lying to the FBI during a terrorism investigation has been ordered detained while his case is presented to a grand jury.

Hamza Ahmed was arrested last week as authorities are investigating people who have gone to Syria to fight with the Islamic State group. Court documents say he and three other men from Minnesota took a bus to New York City in November and tried to travel overseas. All four were stopped.

According to information that came out at a Monday hearing, Ahmed indicated on Twitter that he was willing to martyr himself. U.S. Magistrate Judge Steven Rau ordered that Ahmed remain in custody, saying his tweets were threats.

Authorities say a handful of Minnesota residents have traveled to Syria to fight with militants.