An unidentified person on Monday made a phone call to a hospital in Mumbai and threatened to kill the family of industrialist Mukesh Ambani, a police official said.
The person made three to four calls on a landline number of the Reliance Foundation Hospital in Girgaon area around 10.30 am, he said.
After receiving information about the calls, the Mumbai police initiated a probe into it.
A preliminary enquiry suggested the caller was mentally unstable, the official said. A process was on to register an FIR in this connection, he added.