The St. Cloud Fire Department is investigating the cause of a basement fire that killed a family dog.

St. Cloud Fire Marshal Michael Post says a fire broke out just before 3 a.m. Tuesday morning in the 2200 block of 10th Avenue South.

Post says the fire started on or near a mattress in the basement, but the cause of the fire was not able to be determined based on the physical evidence at the scene.Looking at fire patterns investigators have not been able to determine an ignition source at this time.

A smoke alarm woke up the family and they were able to escape the burning building. However, their dog Mocha, was unable to and died in the fire.