Brazilian police said on Sunday that they had thwarted a bomb attack planned for Lady Gaga's historic concert that drew more than two million people to Copacabana Beach in Rio de Janeiro on Saturday.

The Civil Police of Rio de Janeiro state, working in co-ordination with the Justice Ministry, said the plot was orchestrated by a group promoting hate speech and the radicalization of teenagers, including self-harm and violent content as a form of social belonging.

According to the Rio city hall, 2.1 million people attended the free concert of the American pop icon.

"The suspects were recruiting participants, including minors, to carry out co-ordinated attacks using improvised explosives and Molotov cocktails," the police said in a statement.

The Justice Ministry said the recruiters identified themselves as members of Gaga's global fan base, known as the "Little Monsters."

The operation was based on a report by the ministry's Cyber Operations Lab following a tip-off from Rio state police intelligence, which uncovered digital cells encouraging violent behaviour among teenagers using coded language and extremist symbolism.

A man described as the group's leader was arrested in the southern state of Rio Grande do Sul for illegal possession of a firearm, while a teenager in Rio de Janeiro was detained for storing child pornography.

Authorities carried out more than a dozen search-and-seizure warrants across the states of Rio de Janeiro, Mato Grosso, Rio Grande do Sul and Sao Paulo.