The police in Brazil said on Sunday that they had foiled a plot to detonate explosives at a Lady Gaga concert in Rio de Janeiro, an event that, by some estimates, drew more than two million people.

Rio de Janeiro’s civil police made the announcement a day after Lady Gaga’s free concert on Copacabana Beach. The show proceeded without disruption, and a representative for the pop star later told The Associated Press that she had learned about the threat from news media reports.

The police said the group behind the foiled plot had been recruiting would-be participants, including teenagers, to carry out attacks with improvised explosives and Molotov cocktails. It said the group’s targets included children, adolescents and members of the L.G.B.T.Q. community.