At least 18 people were killed and nine wounded during a massive police drive against drug trafficking in the outskirts of Rio de Janeiro, the Spanish news agency EFE said.
Rio Safety Secretary Jose Mariano Beltrame told reporters that the clashes between police and suspected drug dealers occurred on Wednesday in the north Rio shantytown of Complexo do Alemao and neighbouring Vila Cruzeiro southeast of Brazil.
He did not, however, provide the identities of the dead or any information about the circumstances leading to clashes.
Some residents claimed that at least one of the fatalities was an innocent boy.
Beltrame said that if need be, his office could renew the operation with double the 1,350 heavily armed police officers who occupied Complexo do Alemao in one of the largest law enforcement operations seen here in recent years.
The sweep came two weeks before the start of the July 13-29 Pan-American Games, being hosted this year by Rio, and amid nearly two-month long intense police activity in the shantytown following the May 2 killing of two policemen.
Wednesday's casualties bring to 43 the number of people killed in Complexo do Alemao since early last month.