"After noticing the fatwa post on Thursday, an inquiry has been initiated following the registering of a criminal case at the West Agartala police station," West Tripura district police chief Abhijit Saptarshi told IANS.
He said: "Police registered the criminal case suo-motu under the relevant provisions of Indian Penal Code and Information Technology act. We would seek the help of cyber-crime experts to track the person."
Mr Saptarshi said the post has now been deleted.
The fatwa said a cash reward of Rs 5.5 lakh would be given to anyone for being able to "chop off the head of Chief Minister Manik Sarkar".
Using the name Ria Roy along with a girl's photograph, the account holder introduced itself as an activist of the World Anti-Communist Council. However, there were no personal details in the profile section.