MONTREAL (AP) _ Fire swept through four adjoining apartment buildings in Montreal on Thursday, killing four people including a 15-year-old boy who jumped from a third-floor window, fire officials said.

Fire Chief Yvon Pineau said arson was suspected in the 5 a.m. blaze which left 20 families homeless.

''The fire spread so fast. In my mind, it's not natural,'' Pineau said.

Firefighters discovered the bodies of a 35-year-old man, a 28-year-old woman and a teen-ager in front of a window on the third floor of one of the damaged buildings in the city's East End.

The fourth victim died in the hospital from injuries suffered when he jumped to escape the flames, officials said.

Identities of the victims were not immediately released.

Another resident was injured after apparently jumping to the sidewalk below. Three firefighters were treated for burns and smoke inhalation.

About 100 firefighters brought the blaze under control after five hours.