An Arizona fire official says a trailer house contained rifles and ammunition and likely added to the severity of a fire that killed four people.

Apache Junction Fire Department spokesman Dave Montgomery says investigators aren't sure if the ammunition caused the deadly fire. Investigators are still combing through the blackened remains of the mobile home in the Phoenix suburb.

The victims are an 11-year-old boy and a 7-year-old girl along with two stepbrothers, ages 38 and 32.

Apache Junction Fire Department Battalion Chief Mike Farber tells The Associated Press firefighters responded to a call of an explosion and found the mobile home in flames around 9:30 p.m. Tuesday.