It said those involved had recruited people online to “carry out attacks using improvised explosives” and Molotov cocktails as “a collective challenge with the aim of “gaining notoriety on social media”.

The plot was orchestrated by a group promoting hate speech and teen radicalisation, police say. Source: AFP / Mauro Pimentel

The police added that the group behind the plot “spread hate speech,” radicalised youths, and used self-harm on digital platforms as mechanisms to develop social belonging.

Lady Gaga’s concert was the second million-strong show on Copacabana beach in a year after a huge concert last year by Madonna.

‘Scared sick’

The gig was part of a strategy by Rio to hold mega-concerts in May in an effort to boost tourism during what is considered the low season.