MONTERREY, Mexico (AFP) – At least 17 people were killed in a string of attacks in Mexico, authorities said Sunday, including a shooting at a bar in Monterrey just hours after the opening of soccer's Under-17 World Cup.

Gunmen stormed the bar in Mexico's third largest city late Saturday and "executed three people," wounded another, and kidnapped a security guard at the bar who was later found dead, an official of Nuevo Leon state's investigation agency told AFP.

Four other people, 18-25 years old, were killed Sunday morning in Guadalupe, a city adjacent to Monterrey.

"The victims were gathering in front of one of their homes when armed men showed up in several vehicles and shot them," the official said.

Monterrey is one of the host cities for FIFA's Under-17 football tournament and it held two matches on its opening day Saturday: France-Argentina and Japan-Jamaica.

The relatively prosperous industrial hub of northern Mexico, home to several foreign companies, was until recently considered a near-safe haven as drug violence increased in many parts of the country.

But a bloody turf war between the Gulf cartel and its former hitmen the Zetas has spilled into the state in less than two years, producing daylight shootouts, grenade attacks and a climate of fear.

Thirty-three violent killings were recorded in and around Monterrey, an area of some four million, on Wednesday, making it the area's most violent day in recent history.

Another nine people meanwhile were killed in the western state of Michoacan, whose bodies were found early Sunday, authorities said, also blaming drug cartel-related violence there.

Mexico is in the grip of a brutal wave of largely drug-related violence that has killed some 37,000 people since President Felipe Calderon launched a military crackdown on organized crime in 2006.