MARLBOROUGH, Conn. (AP) An 18-year-old Marlborough man is in the hospital with serious abdominal injuries after an unknown object that had been thrown on a bonfire exploded.

State police say Robert Hill and several other teenagers were gathered at a bonfire at about 9:45 p.m. Sunday when the object, contained inside a plastic bag, was placed in the fire.

The explosion sent fragments flying, some of which struck Hill. No one else was hurt.

Hill was treated at the scene by EMTs and then was flown to Hartford Hospital.

The cause of the explosion remains under investigation.