Union Home Minister P Chidambaram, while officially confirming the death of Andhra Pradesh chief minister YS Rajasekhara Reddy in a helicopter crash, on Thursday said it was not yet known what caused the accident, in which four others were also killed.

"I am officially confirming the tragic deaths," said a sombre Chidambaram, who was supervising the massive search operation for the missing Bell-430 helicopter with which contact was lost at 9.35 am on Wednesday, an hour after it had taken off from Hyderabad on a flight to Chittoor, 588 km south of the Andhra Pradesh capital.