The killing of the officers capped a bloody few days in Michoacan
Twelve people tortured, murdered and dumped alongside a mountain road in Mexico's Michoacan state were federal police officers, officials say.
The bodies of the 11 men and one woman were found tied and blindfolded near the town of La Huacana on Monday.
They had been ambushed by members of a drugs gang, in apparent retaliation for the capture of one of their leaders.
President Felipe Calderon has vowed to continue his war against drugs cartels, and not be intimidated by violence.
He said a wave of attacks on police was a desperate reaction from the gangs to the capture of some of their top leaders.
"The criminals will not be able to intimidate the federal government," Mr Calderon said. "In this battle we will not give up, we will not hesitate, because what is at stake is Mexico's peace and safety."
Michoacan - the president's home state - has been hit by a wave of drug-related killings after a government crackdown on the cartels.
The latest killings, the highest one-day loss suffered by federal forces, marks an escalation in the violence, correspondents say.
The federal agents are believed to have been targeted as revenge for the arrest last week of the suspected drug boss Arnoldo Rueda Medina - known as La Minsa and described as a senior member of La Familia Michoacana drug cartel.
La Familia came to prominence in September 2006 when its members flung five human heads onto a crowded dance floor in Michoacan.
Previously believed to answer to Gulf Cartel, listed as separate group in March 2009 government report
Combines code of violence with idea of protecting people in Michoacan from outsiders
Also involved in counterfeiting, extortion, kidnapping, armed robbery, prostitution, protection rackets
The attackers left behind a bizarre note that said: "The family does not kill for money. It does not kill women or innocent people. Those who die are those who must die. Everyone should know that this is divine justice."
La Minsa's arrest at the end of last week set off a series of attacks, mainly in Michoacan, that left several federal police officers and two soldiers dead.
"This marks an important change in the drug war in that they are attacking federal forces directly," Jorge Chabat, a Mexican drug expert told the Associated Press.
"It also suggests the capture of this person (La Minsa) has affected the operations of the cartel. It was a major blow and this is a reaction out of weakness, not strength."
The state has become one of the key battlegrounds in his war on drugs.
In May, the authorities arrested 27 high-ranking officials, including 10 mayors and an aide to the state governor, who were suspected of collaborating with drug-trafficking gangs in Michoacan.
Police also detained several suspected members of La Familia.
Mr Calderon has sent more than 45,000 troops across Mexico to fight rival drug gangs.
More than 11,000 people have been killed in drug-related violence since he took office in December 2006.
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