NORMAN, Okla. (AP) -- A fire in an apartment unit early Tuesday killed three young children and left an adult in critical condition, firefighters said.

Firefighters found heavy smoke and flames coming from the kitchen of a downstairs apartment at 1:17 AM. A Norman police officer who helped at the fire was treated for minor injuries and released.

Officials said 5-year-old Garrett McClure, Nakayla McClure, 4, and 18-month-old Ariana Clarkson were killed in the fire.

Natasha McClure suffered burns and was listed in critical condition.

The children were believed to have died of smoke inhalation, firefighters said.