The deaths of three people found in a burning house were under investigation Friday by San Diego County authorities.

The fire was reported just before midnight Thursday in an unincorporated area near El Cajon and the structure was fully ablaze when firefighters arrived, the Sheriff's Department said in a statement.

Two people were pulled out by firefighters and rushed to a hospital but both were pronounced dead, the department said.

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A third person was taken to the hospital with injuries that were not life-threatening.

Firefighters then found another person dead inside the home.

The Sheriff's Department said the county medical examiner's office will determine the the victims' identities and cause of death.

The cause of the fire was under investigation by the sheriff's bomb/arson unit, which probes fires involving suspicious circumstances, serious injuries and death, the department said.