PHILADELPHIA — A Taiwanese exchange student accused of threatening a shooting at his suburban Philadelphia high school is facing a federal firearms charge.

Eighteen-year-old An-Tso Sun pleaded guilty Monday to state terroristic threat charges and was sentenced to four to 23 months. He was immediately paroled to federal authorities who announced Wednesday he was charged with felony possession of ammunition while in the country on a non-immigrant visa.

School authorities were alerted in March that Sun talked about a May 1 shooting at Monsignor Bonner and Archbishop Prendergast High School. Sun called it a joke, but prosecutors say ammunition and weapons were found in his home.

Defense attorney Robert Keller says Sun has cooperated fully and he hopes to move the case through the system quickly so Sun can return to Taiwan.