PHILADELPHIA (AP) _ A fast-moving arson fire in a row house killed two young boys early Wednesday, and authorities were investigating the possibility the home was firebombed.

Firefighters found intense flames and heavy smoke coming from the building when they arrived shortly after 4 a.m.

``The fire had really gained too much headway to save anybody,'' Fire Commissioner Harold Hairston said.

The blaze killed two boys, ages 1 and 3, who were sleeping on the first floor, he said.

``It's an arson, so that makes it a homicide,'' said police Sgt. Alexander Strong.

Kevin Abraham, 38, the father of the victims, said he moved out of the house in the North Philadelphia neighborhood two months ago and had been in a bitter custody dispute with his girlfriend. He said he has custody of their third child, a 6-year-old girl.

``I tell my boys I'd never let anything happen to them, and now I have to go home and tell their sister she'll never see her brothers again,'' said Abraham, who cried after looking at the charred house.

The method used to start the fire had not been determined but investigators were considering the possibility that the house was firebombed.

``We're leaning in that direction,'' Strong said. ``We had a witness who did see something.''

Police said a relative who was upstairs when the fire began had argued with several other men several hours before the fire began. The relative told police he heard something come through the first-floor window where the children were sleeping.

The children's mother had not been located, Strong said. He said she had gone on a trip with a male friend, telling neighbors she would be staying in a hotel in New Jersey.

Firefighters rescued two adults with a ladder. They were listed in stable condition at Temple University Hospital.