The government has upgraded the security cover of billionaire industrialist Mukesh Ambani to the top category of `Z+` after a review of perceived threat perception to him by central intelligence and security agencies, official sources said on Thursday.

The 65-year-old Ambani, chairman of Reliance Industries, was first accorded the `Z` category cover of CRPF commandos in 2013 on a payment basis. His wife Nita Ambani too has a similar armed cover but a lower category of `Y+` which entails lesser number of commandos.