Reliance Industries Chairman Mukesh Ambani has received a threat email from an unidentified person seeking ₹400 crore, police said on Tuesday.
Ambani's company received the email on Monday.
It is the third threat email sent to Ambani in four days, an official said.
Earlier, an FIR was registered at Gamdevi police station here based on a complaint filed by the industrialist's security in-charge after the first email, seeking ₹20 crore, was received from an unidentified person on Friday.
On Saturday, the company received another email demanding ₹200 crore.
The company received the third email on Monday, in which the sender doubled the demand, the official said.
The Mumbai police, their crime branch and cyber teams are working to trace the sender of the email, he added.
Last year, the Mumbai police arrested a man from Bihar's Darbhanga for making death threat calls to Ambani and his family members. The accused had also threatened to blow up the Sir H N Reliance Foundation Hospital in Mumbai.