People familiar with the investigation of a UPS plane that crashed in Dubai last week say there appears to have been an in-flight fire in the plane's cargo compartment.

They tell The Associated Press that investigators are now trying to verify which cargo aboard the Boeing 747-400 was located just forward of the starboard wing, where the fire erupted. They also want to know if there were any lithium-ion batteries in that location. If a battery short-circuits, it can catch fire and ignite others.

The people familiar with the investigation asked not to be identified because they weren't authorized to speak publicly about the ongoing investigation.

A data transmission system onboard sent a warning via satellite to UPS' offices before the crash.