Khloe Kardashian is ''not worried'' after being sent a suspicious package of white powder.

The FBI is investigating 'The X Factor' USA set after an envelope was sent to the 28-year-old presenter at CBS' studios in Los Angeles but the 'Keeping Up With The Kardashians' star is not concerned because the show's producers have now hired extra security.

A source close to the reality star turned TV host told E! News ahead of last night's (20.11.12) live show: ''Khloé is fine. The studio has hired extra security. Khloé is heading to rehearsals right now. She is not worried.''

FBI Public Affairs Specialist Laura Eimiller confirmed that law enforcement officers are still investigating the situation despite tests showing that the powder was completely harmless.

She said: ''The item was field tested with negative results. We have a continuing investigation.''

A similar package was previously sent to the same studios addressed to former US Vice Presidential candidate Sarah Palin's daughter Bristol while she was competing on 'Dancing With The Stars.'

Khloe - who is married to Clippers basketball star Lamar Odom - has not publicly commented about the packaged but posted the word ''Awkward'' on her twitter last night.