FBI Investigating Suspicious Package Sent to Dancing With the Stars' Bristol Palin

White, powdery substance involved

The FBI and the LAPD have launched a joint investigation into the suspicious package that was addressed to Bristol Palin at "Dancing with the Stars" this week, TMZ has learned.

Law enforcement sources tell us both agencies are taking the package's threat very seriously and are looking into the possibility that the latest incident is connected to the white powder scare back in 2010.