Brazilian police have thwarted what they described as a planned bomb attack at Lady Gaga's free concert on Copacabana Beach, which attracted a record-breaking crowd of 2.1mn people on April 3 night.

Rio de Janeiro's Civil Police, working in coordination with Brazil's Ministry of Justice, arrested a man identified as the leader of the criminal group behind the plot, along with a teenager. The operation, codenamed "Fake Monster" – a reference to Lady Gaga's affectionate name for her fans, "Little Monsters" – involved search and seizure warrants across multiple Brazilian states.

According to police, the suspects were recruiting participants online, including teenagers, to carry out coordinated attacks using improvised explosive devices and Molotov cocktails. Officials said the group treated the plan as a "collective challenge" aimed at "gaining notoriety on social media".

"The police acted silently and without creating panic... We acted surgically to prevent the crime from happening," said Felipe Curi from Rio de Janeiro's Civil Police in a statement, as quoted by AFP.

The group allegedly spread hate speech against children, adolescents and the LGBTQ+ community, whilst promoting radicalisation and self-harm online using coded language and extremist symbolism.

Authorities said the adult suspect was arrested in the southern state of Rio Grande do Sul for illegal possession of a firearm, whilst a teenager was detained in Rio de Janeiro for storing child pornography. A third suspect in Macaé, in Rio's Lakes Region, was the target of a search and seizure operation after allegedly threatening to kill a child during a livestream.

Police carried out fifteen search and seizure warrants across Rio de Janeiro, São Paulo, Rio Grande do Sul, and Mato Grosso states. In São Vicente, São Paulo, a 16-year-old teenager was identified as the author of some of the hate messages published online, according to São Paulo Civil Police. Authorities seized electronic devices from the teen, who was later released to his father.

The threat was initially identified by the Rio police intelligence unit, with Brazil's Justice Ministry's Cyber Operations Laboratory producing a technical report on the digital threats.

Lady Gaga's team said in a statement to the Associated Press that they "became aware of this alleged threat through press reports" on the morning of April 4, after the concert had concluded. "Prior to and during the show, there were no known safety concerns, nor any communication from police or authorities to Lady Gaga about any potential risks," the statement continued.

The concert, Lady Gaga's first in Brazil since 2012, was part of Rio's strategy to boost tourism during what is traditionally considered the low season. Security was tight, with approximately 5,000 officers deployed alongside drones and surveillance cameras.

The 39-year-old pop star thanked her Brazilian fans on social media for "the biggest crowd for any woman in history". The show featured the singer performing several tracks from her latest album, "Mayhem", as well as major hits from throughout her career.

Rio Mayor Eduardo Paes has announced plans to bring other major international acts to the city, including Irish rock band U2, though no date has been set.