Brazil must redouble efforts to end "inhumane conditions" in its prisons and the "unlawful use of lethal force" by police, Human Rights Watch said in its annual report Tuesday.
The HRW report, released here as well as in several other world cities, said gruesome prison killings in the northern state of Maranhao last month "highlighted a wider problem of violence in Brazilian detention centers."
Four inmates died in a December 17 fight at Pedrinhas Penitentiary in the northern state of Maranhao.
The release of video footage showing three decapitated inmates at the Pedrinhas prison triggered UN calls for a "prompt, impartial and effective investigation."
Maranhao state authorities on Tuesday reported another death at the Pedrinhas facility, where an inmate was found hanging in his cell by a sheet.
Brazil, which reportedly has the world's largest prison population, has seen the number of incarcerations climb by a staggering 380 percent over the past 20 years.
The New York-based HRW also accused Brazilian police of brutality, saying they "used force disproportionately against protesters" during last June's nationwide street demonstrations demanding a better quality of life and an end to widespread government corruption.
The Brazilian government "needs to double up on its efforts to address grave violations at home such as the use of force against protesters, unlawful police killings and torture," HRW's Brazil director Maria Laura Canineu told a press conference.
She also expressed HRW's "deep concern over growing violence against the country's indigenous population."
She pointed to a report by the Indigenous Missionary Council (CIMI) last year recording 60 deaths of indigenous people across Brazil in 2012, mainly in land disputes.
The figure, which included 43 deaths in central Mato Grosso do Sul state, was up from 51 the previous year, CIMI said.
Indigenous Brazilians represent less than one percent of the country's 200 million people and occupy 12 percent of the national territory, mainly in the Amazon.
They have been trying to recover a small portion of their ancestral lands, but face violent resistance from wealthy ranchers as well as soya and sugar cane plantation owners.
HRW, however, acknowledged that Brasilia has taken various important measures to improve its human rights record, including a mechanism to combat and prevent torture and a constitutional amendment to strengthen the rights of domestic workers.
Canineu added that "with its increasingly prominent place on the world stage, Brazil has the potential to play a much more active role in promoting international efforts to curb serious human rights violations."
She notably hailed Brasilia's leadership role in defending the right to privacy in the wake of revelations of global US electronic spying.
Brazil was angered last year by disclosures that the US National Security Agency snooped on its government communications, those of state-run energy giant Petrobras, as well as phone call data and emails of millions of Brazilians.
Those disclosures, based on leaks from Edward Snowden, a former US intelligence contractor, led Brazilian President Dilma Rousseff to reprimand the United States at the UN General Assembly session in September and to cancel a planned state visit to Washington.
Brazil and Germany also jointly sponsored a resolution on the protection of individual liberties at the UN General Assembly's human rights panel in New York.
Canineu, meanwhile, urged the Brazilian government to play a greater role in addressing human rights violations in strife-torn Syria.
"Brazil has played a constructive role at the United Nations in several debates over international responses to human rights crises," HRW said.
"However, this positive engagement was overshadowed by its decision not to support a call for the (UN) Security Council to refer the situation in Syria to the ICC (International Criminal Court)," it added.