A house fire killed three young brothers during the night and critically injured their grandmother, who apparently tried to rescue them, authorities said Tuesday.

The blaze in rural Hartland, about 25 miles northeast of Buffalo, remained under investigation but appeared to have been accidental, said Niagara County Fire Coordinator Jim Volkosh.

The fire was reported shortly after 11 p.m. Monday and the house was engulfed in flames when sheriff's deputies and volunteer firefighters from six area companies arrived.

They tried to rescue the boys but the smoke and flames were too intense, Volkosh said.

The boys' grandmother, 59-year-old Leona Heigl, apparently tried to re-enter the house to rescue the boys, Volkosh said. Heigl was overcome by smoke and was listed in critical condition Tuesday at Erie County Medical Center in Buffalo.

All three boys were trapped in the downstairs part of the house, firefighters said.