PHILADELPHIA (AP) — A fight aboard a bus traveling in Philadelphia early Thursday ended with a man shooting three teenage boys in their legs, authorities said.

The 24-year-old shooter was sitting in the back of the Southeastern Pennsylvania Transportation Authority bus when he was approached around 1 a.m. by two 16-year-olds and a 17-year-old, authorities said. The four began arguing and the dispute soon turned physical, authorities said.

The man, who authorities said had a concealed weapons permit, soon opened fire and shot the youths. The teens were all being treated at hospitals, but further details on their conditions were not disclosed.

The man, who told police he acted in self-defense, was not seriously injured in the fight. The bus driver and a few other passengers aboard the bus were not injured, authorities said.

It's not clear what sparked the argument, authorities said, or if any charges would be filed.