Rio De Janeiro, May 25 : At least 21 people were killed and four injured in a police operation against drug trafficking in a favela in Brazil's Rio de Janeiro, the Military Police said. The police operation took place on Tuesday, Xinhua news agency reported. The event occurred in Vila Cruzeiro during an operation by the Federal Police, the Federal Highway Police and the Military Police, which was aimed at capturing the heads of the largest criminal faction in the city. According to the Military Police, the agents were met with gunfire in the upper part of the favela. They responded and left at least 11 suspects dead. A 41-year-old woman was killed by a stray bullet, while nine more bodies were unidentified. During the operation, 11 rifles, four pistols and a grenade were seized, as well as a large quantity of drugs, 10 vehicles and 20 motorcycles used by local drug traffickers. /IANS