MEXICO CITY -- The revelation that as many as 27,000 people may have gone missing in Mexico in recent years renews attention to the huge human toll left by the war on crime that former President Felipe Calderon waged during his six years in office.

Combined with the 70,000 dead acknowledged recently by the new administration of President Enrique Pena Nieto, who succeeded Calderon on Dec. 1, the number of the disappeared makes the Calderon tenure the bloodiest period in Mexican history since the Mexican Revolution of the early 20th century.

On Thursday, human rights campaigners said the numbers place Mexico far above some of the better-known Latin American human catastrophes of decades past, including the rule of military regimes in Argentina, Chile and Brazil and civil wars in Nicaragua and El Salvador.

Lia Limon, Mexico’s deputy interior secretary for human rights and legal affairs, acknowledged on Wednesday that the government had compiled a list of 27,000 missing people after meeting with representatives of the New York-based advocacy group Human Rights Watch.

Mexican Interior Secretary Miguel Angel Osorio Chong on Thursday promised to “look for all of them.” But he also warned there were no guarantees. “We start from a fundamental fact,” he said, “little information, little evidence and no rules.”

Civic activists hailed the government for disclosing the list, nonetheless.

“It is an acknowledgement by the Mexican state of the problem,” said Jorge Verastegui Gonzalez, spokesman for United Forces for Our Disappeared in Mexico, an advocacy group. “Recognition is a first step.”

Jose Miguel Vivanco, executive director of Human Rights Watch’s Americas division, said any list of disappeared must be carefully scrutinized and cross-checked to eliminate those who are known dead or who later reappeared. He said that even if a final tally is smaller, the numbers are “overwhelming.”

Over the past six years, Vivanco said, Mexican authorities have collected 15,921 bodies or partial human remains that have never been identified.

“These figures speak for themselves,” he said at a news conference, adding that “in terms of forced disappearances, the numbers put Mexico almost at the vanguard of what lamentably has occurred in Latin America in this area.”

“How many people disappeared during the military dictatorship in Brazil? According to official figures, 137 people,” Vivanco said. “How many disappeared in Chile? The most recent official figures say around 3,000. How many disappeared in Argentina during the military dictatorship? According to the Sabato report ‘Never Again,’ around 10,000 people.”

In a detailed report released this week, Vivanco’s group said that it had investigated 249 cases of disappearances in Mexico. Of those, 149 involved people who witnesses saw being detained by military personnel or municipal, state or federal police. He said the actual number of such cases is certainly far higher, though what proportion of the total number of disappeared had government involvement is not clear.

Organized crime syndicates are thought to be responsible for the bulk of Mexico’s bloodshed, unleashing a wave of terror that included beheadings, dismemberments and public executions in a battle fueled by cash from an insatiable demand for cocaine and other drugs in the United States.