Thousands of people have taken part in an anti-femicide protest in Buenos Aires, demanding justice for a girl and two young women who were tortured and murdered in a crime that has shocked Argentina.

The brutal killings of 15-year-old Lara Gutierrez, and Morena Verdi and Brenda del Castillo, who were both 20, were livestreamed on social media.

Police believe a drug-trafficking gang was responsible, and that the crime was broadcast as a warning to others.

They had arrested five suspects – three men and two women – as of Friday, according to National Security Minister Patricia Bullrich, but a 20-year-old Peruvian man they say is the group's leader remains at large.

The victims were lured into a van believing they were headed for a party on 19 September, according to investigators.

But authorities said this was part of a plan to “punish” the girl and young women for violating gang code, serving as a warning to others.

One of the detainees revealed a video of the incident under questioning, according to Javier Alonso, security minister for the Buenos Aires province.

In it, a gang leader is heard saying: “This is what happens to those who steal drugs from me.”

Authorities have released a photograph of the alleged Peruvian mastermind in the hope he is recognised.

The bodies of the three victims were found buried at a property in a southern suburb of Buenos Aires on Wednesday, five days after they went missing.

In Buenos Aires, relatives of the victims joined a march to Parliament on Saturday demanding justice for the women and girl.

“Women must be protected more than ever,” Brenda’s father, Leonel del Castillo, told reporters at the protest.

He had earlier said it was impossible for him to identify his daughter’s body due to the abuse inflicted on her.

Antonio del Castillo, grandfather of the 20-year-old cousins, was in tears, as he called the killers “bloodthirsty”.

“You wouldn’t do what they did to them to an animal,” he said.

One woman is killed by a man every 36 hours in Argentina, according to a femicide monitoring group in the country cited by Agence France-Presse. (BBC)