The Civil Police of Rio de Janeiro state, working in coordination with the Justice Ministry, said the plot was orchestrated by a group promoting hate speech and the radicalisation of teenagers.
According to the Rio city hall, 2.1 million people attended the concert of the American pop icon on Saturday.
"The suspects were recruiting participants, including minors, to carry out coordinated attacks using improvised explosives and Molotov cocktails," the police said in a statement on Sunday.
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 over a dozen search and seizure warrants across the states of Rio de Janeiro, Mato Grosso, Rio Grande do Sul and Sao Paulo.
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