MEXICO CITY -- Mexico's most feared drug cartel was already known for beheading, quartering and even cooking its enemies, in the brutal narcotics war gripping the country.

Now the Zetas gang is said to have created a new gladiator-like sport where innocent kidnap victims are forced to fight to the death, according to sources cited by The Times of London on Wednesday.

Members of the cartel are said to have dubbed the sadistic spectacle "Who wants to be the next hitman?"

Victims are armed with hammers and machetes and goaded into fighting for their survival and the chance to work as assassins. The alleged practice has been linked to mass graves where the remains of more than 400 people have been unearthed in recent months.

"We've been given several suggestions that this kind of activity happens," a source at the US Drug Enforcement Agency told The Times.

A source with links to the drug trade said he had heard detailed accounts of the new blood sport. "The violence has reached such a level, even the gangsters are getting sick of it," he added.

Mexico's northern border regions have suffered an explosion of violence as government forces battle the Zetas -- a drug gang formed in the 1990s by former soldiers -- and their former bosses, the powerful Gulf cartel, in a three-way war.

The conflict has claimed nearly 35,000 victims in the past five years, according to official figures, but the true toll may never be known. Since 2006 at least 5,300 Mexicans have disappeared. Witnesses have reported seeing large groups of people being snatched from intercity buses by gangs who appear to act with impunity.

Some kidnap victims have had one hand handcuffed to a car steering wheel, and a gun placed in the other, to be sent on murder missions. Others have been found hanged in the streets. Most of 200 bodies discovered in mass graves in the northeastern state of Tamaulipas were of victims apparently killed with sledgehammers or burnt alive.

A report in the Houston Chronicle, which drew on an account from an anonymous drug runner, said: "The elderly are killed. Young women are raped. And able-bodied men are given hammers, machetes and sticks and forced to fight to the death."