* Suspected drug hitmen kill six men on U.S. border

* Hitmen kill police chief near wealthy Monterrey

* Attacks latest violence in escalating drug war (Updates with killing of police chief in northern Mexico)

By Julian Cardona

CIUDAD JUAREZ, Mexico, Nov 4 (Reuters) - Gunmen with automatic weapons burst into a Mexican strip club on the U.S. border, opened fire on patrons and killed six people including an American soldier, the army said on Wednesday.

The hooded gunmen stormed into the bar in Ciudad Juarez as strippers were dancing for customers, sought out the six men and shot them each several times. A 26-year-old off-duty U.S. soldier who had crossed over from El Paso, Texas, was among the dead, army spokesman Enrique Torres said.

"It appears drugs were being sold at the place," Torres said of the strip joint. "The hitmen went directly for their victims, no one else."

The suspected drug hitmen escaped the bar easily, while panicking customers fled in their cars as pools of blood gathered around spent bullet cases on the bar floor.

In a separate assault near the wealthy northern city of Monterrey, around 30 suspected drug hitmen killed a municipal police chief just five days after he took up his post, and left a threatening warning for the local mayor, police said.

The heavily armed convoy killed Juan Arturo Esparza, a retired general picked over the weekend to head the police force in the municipality of Garcia.

Four other people traveling with Esparza, including two bodyguards, also died in Wednesday's attack.

Moments beforehand, the hitmen left a written message at the house of Garcia's mayor saying: "be careful."

MOST VIOLENT CITY

Across Mexico, the drug war has killed some 15,000 people since President Felipe Calderon launched his army-backed campaign against the powerful cartels in late 2006.

Ciudad Juarez is reckoned to be one of the world's most violent cities as it has become the bloodiest flashpoint in Mexico's three-year fight against feuding drug cartels.

As cartels fight over the city's local drug market and smuggling routes into the United States, dealers, addicts, cops and hitmen are all targeted by rivals in a spiraling and increasingly chaotic drug war.

Dozens of bars and drug rehab clinics have been attacked by drug hitmen this year and more than 2,000 people have died in drug violence in Ciudad Juarez in 2009 despite the presence of 10,000 troops and federal police sent in to stop the killings.

A recent Mexican study put the city's homicide rate higher than notorious murder capitals including Venezuela's Caracas, the U.S. city of New Orleans and South Africa's Cape Town.

Despite U.S. anti-drug aid for Mexico, the escalating conflict, a major concern in Washington, threatens to overwhelm Mexican state security forces as wealthy cartels have amassed huge arsenals of weapons and grenades.

The violence has scared tourists away from border cities like Ciudad Juarez and Tijuana just as Mexico is reeling from its worst economic recession since the 1930s. (Additional reporting by Mica Rosenberg in Mexico City; Editing by Todd Eastham)

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