Drug cartels and other criminals, at times colluding with Mexican authorities, killed and abducted thousands of people last year, Amnesty International said in its annual report.
The London-based rights watchdog also highlighted a panorama of greater threats to indigenous people's human rights in many countries across Latin America.
But Mexico's drug violence -- from the eye-popping bloodshed and its deepening social toll -- stood out as the most glaring human rights disaster in sheer scope in the Americas.
The Mexican government "did not take effective measures to prevent or investigate widespread grave human rights violations committed by the military and the police, including forced disappearances, extrajudicial executions, torture and arbitrary arrests," the report, released on Wednesday, said.
"The criminal justice system failed to deliver justice or security," it stressed in a damning assessment of a situation that has spiraled from bad to worse and even worse.
More than 50,000 people have been killed in drug-related violence since President Felipe Calderon launched an all-out war against the nation's drug gangs upon taking office in December 2006, according to Mexican figures.
Corruption among security forces and police cooperation with the cartels -- often through bribes and threats -- has become a massive problem for authorities that battle the smuggling of illegal narcotics to consumers in the United States.
In Mexico, "those responsible for the vast majority of the crimes, including attacks on journalists, human rights defenders and women, were not held to account," the report said. "Fair trial standards were breached."
Elsewhere in the Americas, with global metal prices sky-high, mining and other extractive industries were increasingly clashing with traditionally isolated indigenous communities.
"In many cases, indigenous peoples were denied their right to meaningful consultation and free, prior and informed consent, over large-scale development projects, including extractive industries, affecting them," the report said.
"The failure to respect the rights of indigenous peoples ... also resulted in communities being threatened, harassed, forcibly evicted or displaced, attacked or killed as the drive to exploit resources intensified in the areas where they live. In Brazil, Colombia, Guatemala and Mexico, indigenous peoples were forced off their lands, often violently."
Amnesty did note that Peru passed a law in 2011 to guarantee consultations before development projects can proceed on native ancestral lands. "However, this remained the exception," the report said.© ANP/AFP