The bodies of eight men were found in Moris, a town in the Tarahumara mountains of the northern Mexican state of Chihuahua, officials said.

The victims, who ranged in age from 19 to 30, were attacked last Saturday by at least 10 gunmen, Chihuahua state Attorney General's Office spokesman Carlos Gonzalez said.

Only four of the victims have been identified and investigators have not determined the motive for the killings, Gonzalez said.

Nine bullet casings from an assault rifle were found at the crime scene along with an SUV that had several bullet holes in it, the AG's office spokesman said.

Chihuahua is Mexico's most violent state and home to Ciudad Juarez, a gritty border metropolis located across the border from El Paso, Texas, where more than 900 people have died in drug-related violence this year.

The northern state has accounted for about 30 percent of the more than 40,000 murders committed in Mexico since late 2006, when President Felipe Calderon declared war on Mexico's drug cartels.

More than 8,500 killings have occurred in Ciudad Juarez alone during since the end of 2006.

Ciudad Juarez first gained notoriety in the early 1990s when young women began to disappear in the area.

In most of the slayings, the victims were young women from poor families who came to the border city from all over Mexico to work in the many assembly plants, known as "maquiladoras," built there to take advantage of the North American Free Trade Agreement, or NAFTA.

Investigators have not determined who is behind the killings, although there has been speculation that serial killers, organized crime groups, people traffickers, drug smugglers and child pornographers, among others, may be involved.