The Haryana Police is investigating alleged threat letters issued to some people, including media persons, by the 'Qurbani Gang' of Dera Sacha Sauda, police sources said on Thursday.Vishwas Gupta, ex-husband of Honeypreet Insan, some former Dera followers speaking against the sect and its disgraced chief Gurmeet Ram Rahim Singh, apart from a few media persons, have been issued these threat letters.The sources said a few people had received threat phone calls from numbers from abroad.Gupta lodged a complaint with the Haryana Police and sought more security.Haryana Additional Director General of Police (Law and Order) Mohammed Akil confirmed that the threat issue was under probe.The 'Qurbani Gang' members are said to be staunch followers trained to sacrifice their lives for the sake of the sect and its chief.Ram Rahim was convicted by a CBI court in Panchkula on August 25 for the rape of two female disciples.He is lodged in the District Jail in Sunaria near Rohtak after he was sentenced to 20 years of rigorous imprisonment.