Whitney Houston's refusal to fasten her seatbelt on a flight yesterday (12.10.11) has been blamed on exhaustion.

The troubled star - who has battled alcohol and cocaine addictions in the past - was almost kicked off a Delta Airlines flight in Atlanta, Georgia, when she refused to buckle up before the plane took off, despite warnings from staff onboard but pals have insisted she is still clean and sober and was merely "exhausted".

A source told People: "She wasn't drunk, drinking or on drugs; she was just exhausted."

Whitney - who is believed to have missed a flight earlier that day - eventually allowed a member of staff to fasten the device for her and the plane was cleared for take-off.

Despite previous substance abuse problems, Whitney's career has been showing positive signs of recovery recently and it was revealed earlier this year that she is set to return to the big screen for the first time in 15 years.

Whitney is set to be reunited with her former 'Waiting To Exhale' castmates to create a sequel to the 1995 hit movie, in which she played unlucky-in-love television producer Savannah Jackson.

Angela Bassett - who portrayed Bernadine Harris in the film - explained director Forest Whitaker is in the process of altering author-and-screenwriter Terry McMillan's follow-up to the movie.

She said: "It's preliminary, but it's going to happen, 'Waiting to Exhale 2'. McMillan wrote 'Getting to Happy' and she's written the screenplay ... Loretta Devine, Lela Rochon, Whitney, Forest. Forest is working on the script now."