Brazil's interim president Michel Temer has ordered crisis talks with the country’s security ministers after the emergence of a video appearing to show a teenage girl being gang raped in Rio de Janeiro.
Mr Temer vowed to form a federal police unit to deal with violence against women, as hundreds of protesters demanded an end to sexual violence.
Mr Temer, who is standing in as the country's leader while Dilma Rousseff is suspended and facing an impeachment trial, said in a statement: "I condemn most forcefully the rape of the teenager in Rio de Janeiro."
"It is absurd that in the 21st Century we should have to live with barbaric crimes such as this."
He said the authorities were working "to find those responsible" for the attack.
The girl, 16, says she went to her boyfriend's house. But woke up the next day in a different house, naked and wounded, surrounded by 30 men. The 40-second video of the attack was put on social media, before being taken down after widespread condemnation.
Police are hunting more than 30 male suspects. Arrest warrants have been issued, including one for the victim’s boyfriend.
Fernando Veloso, Rio de Janeiro's police chief, told a news conference that investigators will review the forensic evidence available.
He said: "If these images hadn't been posted, maybe we wouldn't be here right now,.'
In a message posted on Facebook, the victim said she was thankful for the support she had received and added: "I really thought I was going to be badly judged."
She added: "All of us can go through this one day. It does not hurt the uterus but the soul because there are cruel people not being punished!! Thanks for the support."
The girl's grandmother told Brazilian media the family had cried afer watching the video.
She told Folha de S Paulo newspaper: "I regretted watching it. When we heard the story we didn't believe what was happening. It's a great affliction. It's a depressing situation."
The United Nations group UN Women issued a statement calling for authorities to investigate the case, but to respect the victim's privacy.
The budget for police and special forces that heavily patrol the favelas was cut by about $550 million (£376 million) this year, despite significant spending on the Olympic Games.
There were 4,725 rapes registered in Rio de Janeiro during 2014 – an average of 13 per day, according to Marcelo Freixo, president of the Human Rights Commission of Rio de Janeiro. But it is estimated only 35 per cent of rape cases in Brazil are reported.
On Twitter, the hashtag #EstuproNuncaMais (#RapeNeverAgain in English) trended worldwide.
Demonstrators gathered in Rio de Janeiro on Friday night, waving signs saying "Machismo Kills" and "No means no." In Sao Paulo, placards were held with a message that read "My body is not yours."
Dilma Rousseff, Brazil's first female president, expressed outrage over the Rio case by changing her profile picture on Facebook.
Ms Rousseff wrote: "Once again I reiterate my repudiation to violence against women. We need to fight, to expose and punish this crime.
"It is unacceptable that crimes like this continue to happen. I repeat, we must identify and punish those responsible."