BLUE GRASS, Iowa -- Police say all four people killed by an early Christmas morning house fire in eastern Iowa belonged to one family.

The blaze erupted a little after 12:30 a.m. Monday at a ranch-style house in Blue Grass.

"One of the occupants was able to exit the residence and was transported to the hospital but later passed away. The three other people that were inside the home were unable to escape and perished inside," police said in a statement.

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Blue Grass police Sgt. Garrett Jahns said Tuesday that he couldn't release any of the victims' names or ages yet, but he confirmed that the four were related. Blue Grass is a community of about 1,500 residents 150 miles east of Des Moines.

State and local police say they are still investigating the cause of the fire.