An unidentified person on Monday made phone calls to a hospital in Mumbai and threatened to kill the family of industrialist Mukesh Ambani, a police official said.
The Mumbai police later detained a suspect, he said.
The person made three to four calls on a public 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.
The police later detained a suspect from Dahisar area in connection with the threat calls, he said.
A process was on to register an FIR at the D B Marg police station in connection with the matter, he added.
In February last year, a sports utility vehicle (SUV) laden with explosives was found near Ambani's residence 'Antilia' in Mumbai. Later, some people including police officials were arrested.