GLENDALE, Ariz. -- Glendale firefighters found 15 illegal immigrants in a burning drop house Thursday morning.

A neighbor called 911 shortly after 6 a.m. to report the fire, which firefighters said started in the attic and appeared to have been caused by an electrical problem.

The firefighters called police after they forced their way into the burning home and discovered the immigrants, one of whom was seven months pregnant.

None of the immigrants were injured, though the pregnant woman was taken to a hospital for precautionary reasons, firefighters said.

Immigration and Customs Enforcement is investigating the incident.