Human Rights Watch charged Wednesday that Mexican security forces were not properly investigated over at least 249 "disappearances" that occurred during President Felipe Calderon's government.
"Mexico's Disappeared: the Enduring Cost of a Crisis Ignored," said the people went missing during the Calderon administration, which lasted from 2006 until late last year, and are presumed dead.
The former leader sent in thousands of federal security troops in a bid to crush the country's warring and brutal drug cartels, in a campaign that left tens of thousands of innocent civilians dead in the crossfire.
The rights monitor said in its 193-page report that security forces had been involved in disappearances since 2007, which it had documented, and called on the country's new government to account for the missing.
"In more than 140 of these cases, evidence suggests that these were enforced disappearances, meaning that state agents participated directly in the crime, or indirectly through support or acquiescence," the New York-based group said.
"These crimes were committed by members of every security force involved in public security operations, sometimes acting in conjunction with organized crime.
"In the remaining cases, we were not able to determine based on available evidence whether state actors participated in the crime, though they may have."
The report warns that while there were at least 249 reported cases, after 2007, there may have been thousands of others, citing government documents leaked to local media which estimate the number at up to 25,000.
The war against cartels that Calderon stepped up "produced disastrous results," the report said.
"Not only had it failed to rein in the country's powerful criminal groups, but it had led to a dramatic increase in grave human rights violations committed by the security forces sent to confront them."
It added: "Rather than strengthening public security, these abuses had exacerbated a climate of violence, lawlessness, and fear."
More than 70,000 people were killed during the effort, according to official data.
President Enrique Pena Nieto, with the Institutional Revolutionary Party, took power in Mexico on December 1.
The new leader has said he wants to change the military's role in fighting organized crime, but his overall strategy is yet to be outlined in detail.
The Human Rights Watch report is due to be released officially on Thursday, but the group's Americas chief, Jose Miguel Vivanco, met Wednesday with Mexican Interior Minister Miguel Angel Osorio Chong to discuss it.