Police Wednesday registered a case in connection with threatening calls and a letter received by Telangana Rashtra Samithi (TRS) chief K. Chandrasekhara Rao.
A case against unidentified people was registered by the Banjara Hills police station, a day after a TRS leader lodged a complaint.
The letter received Monday in the name of "Andhra Naxals" threatened to kill Rao in 10 days.
TRS has sought "Z-plus" security for the party leader.