|Mexico's navy seized a massive weapons arsenal while conducting a routine check on a highway in Coahuila [AFP]
Police in the western Mexican city of Morelia have found the bodies of 21 men next to notes identifying them as criminals and warning of more killings to come.
The victims, thought to be aged between 20 and 35, were laid out in groups near the five main highway exits to Morelia, the capital of Michoacan state and where President Felipe Calderon was born and served as governor.
A spokesman for the Michoacan state prosecutors' office said it was too early to say who was behind the killings, which could end up on the tally of more than 38,000 deaths attributed to the war on drug cartels that Calderon declared after taking office in 2006.
Warning notes were left next to the bodies, some of which showed signs of torture, authorities said.
"Because society demands it, here are the thieves, muggers and rapists, and there are still more to come," one read.
Michoacan has been plagued by sporadic violence and is home to one of Mexico's most notorious cartels, La Familia.
On Wednesday, Mexico's navy arrested five men in possession of a massive weapons arsenal while conducting a routine check on a highway in the northern state of Coahuila.
After being stopped at a checkpoint, the suspects aged between 18 and 33, admitted they worked for the feared Zetas drug gang after troops discovered counterfeit uniforms on board the vehicle they were travelling in.
The men then led naval troops to another location where the weapons cache - including 204 rifles, 11 guns, hundreds of cartridges, chargers, as well as seventeen hand grenades - were found.
"Personnel went to the indicated location where they found a cargo vehicle with capacity to carry up to four tonnes. It was partially hidden among some trees. Upon further inspection a weapons arsenal, which was presumably used to train members of the Zetas criminal organisation in the area, was found inside," Rear Admiral Jose Luis Vergara told a news conference in Mexico City on Thursday.
In a separate incident, policemen rescued a man who had been hung from his wrists by suspected drug gangs in the northern city of Monterrey on Wednesday.
Dramatic video footage showed the desperate man shouting for help. The lifeless body of another victim hung beside him with a shot to the head.
Paramedics were the first to arrive at the scene and tried to rescue the man. As they were trying to do so, hooded gunmen returned to the scene and threatened them by firing shots into the air.
The drug-related violence has sparked national protests in Mexico, hurting Calderon's conservative National Action Party (PAN) and stirring fears that tourism and investment could suffer in the world's seventh biggest oil exporter.
Calderon's approval rating has recently slipped below 50 per cent for the first time, pollster Mitofsky said.
Michoacan holds a state election in November, and Luisa Maria Calderon, the president's elder sister, is among the PAN front-runners expected to seek the office of governor.
Daily newspaper Milenio said that Wednesday was the third most violent day on record since Calderon took office.