The bodies of seven men, all shot in the head as if executed, were found dumped in plastic chairs placed along the side of a street in the Mexican state of Michoacan, authorities have said.

Michoacan's attorney general's office said in a statement on Saturday that the victims had all been shot in the head and placed individually in the sitting position in chairs near a traffic circle in the city of Uruapan.

A placard nailed to one of the bodies with an ice pick reads: "Warning! This will happen to thieves, kidnappers, sex offenders and extortionists".

The office did not provide a motive for the killings.

It comes after seven people were killed in neighbouring Guerrero state when armed men opened fire in a bar in Ciudad Altamirano on Friday evening.

Four civilians and three off-duty federal agents were among those killed.

Surge in violence

Both states on Mexico's western coast have seen a surge of violence in recent years attributed to drug cartels.

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Drug violence escalated after former president Felipe Calderon launched a nationwide crackdown against narco-traffickers.

An estimated 70,000 people have been killed in drug-related violence in Mexico in the past seven years.

The Mexican government estimates that at least another 26,000 have "disappeared" in that same period.

President Enrique Pena Nieto, who took office in December, has vowed to quell the lawlessness and killing that have stained Mexico's image as a tourist destination and rattled investors.

Thousands of soldiers were sent to patrol the streets, but the number of fatalities continued to rise.

Human rights groups accuse government forces of being behind hundreds of cases of missing people.

Source: Agencies