The United Nations human rights office has strongly criticised a police raid against suspected drug traffickers in Rio de Janeiro, amid allegations of abuse and extrajudicial executions.
The deadliest police operation in the city's history has left 25 dead, including a police officer.
Residents say police killed suspects who wanted to surrender and entered homes without a warrant.
Police have denied any wrongdoing, saying officers acted in self-defence.
Vast areas of Rio de Janeiro, one of Brazil's most violent cities, are under the control of criminals, many of them linked to powerful drug-trafficking gangs. Security forces are often accused of disproportionate force during their anti-crime operations.
Thursday's raid in Jacarezinho, one of the city's largest slums, known as favelas, was carried out by about 200 police officers and an armoured helicopter with a sniper. The area is controlled by one of Brazil's largest criminal organisations, the Comando Vermelho, or Red Command.
A television helicopter filmed heavily armed suspects jumping from rooftops, while desperate residents posted videos on social media showing intense shootouts as they claimed police invaded their houses and used excessive violence.
"There are boys who have been cornered in the house and want to surrender," one resident said, referring to the suspects. "And the police want to kill them. They have even killed some in front of us."
In another video, a resident filmed a police officer standing next to a house and said: "They're cornering [the suspects]. They don't want to let the boys surrender."
'Lots of pools of blood'
Public defender Maria Júlia Miranda said residents told her a suspect was killed in the bedroom of an eight-year-old girl where there were blood stains on the floor and on her bed, and that the family had witnessed the alleged execution.
Ms Miranda said she was "shocked" by seeing "lots of pools of blood... and walls with bullet marks" when visiting the favela. There was also evidence that the scenes of the killings were not preserved, with bodies being removed, she said. "On these cases, there was probably an execution."
Human rights groups, including Amnesty International, said they had also received reports and images from residents saying that police officers had invaded their houses, and that people had been killed when they already offered no risk.
"It's completely unacceptable that security forces keep committing grave human rights violations such as those that occurred in Jacarezinho against residents of the favelas, who are mostly Black and live in poverty," Jurema Werneck, executive director of Amnesty International Brazil, said in a statement, calling it a "massacre".
The United Nations human rights office called for an independent investigation, describing it as a "long-standing trend of unnecessary and disproportionate" police operations against predominantly poor communities.
"You have the institutions which control these operations... So, it appears that collectively, they are not succeeding in stopping these kind of really disturbing, over-the-top, lethal operations. So something is clearly wrong there," said spokesman Rupert Colville.
The officer killed was named as Inspector Andre Leonardo de Mello Frias, who was shot in the head while trying to remove a barricade allegedly set up by the criminals. Police have not yet identified the suspects killed but said six other people were arrested.
Deputy Police Chief Rodrigo Oliveira defended the police's actions, saying that officers acted within the law. "The only execution that took place was that of the police officer," he said at a news conference.
Police say they launched the operation to serve 21 arrest warrants as part of a year-long investigation that suggested gangs were recruiting children. Experts again questioned the force used given that minors are used by criminals across the city.
"This is cruel, barbaric," Joel Luiz Costa, a lawyer from Jacarezinho, said in a video posted on Twitter. "Twenty-five people or more were killed. Did it end drug trafficking? Will this end drug trafficking?"
The raid happened despite a court ruling last June that restricted police action in poor areas of Rio during the pandemic unless it was deemed essential. The Rio state public prosecutor's office said it would launch an investigation while the police said they would also open an inquiry.
Far-right President Jair Bolsonaro, a former army captain, has not commented. He supports changes in legislation that would protect officers from prosecution if they kill suspects, and has previously said that "a good criminal is a dead criminal".