Families were out for the night air, taking a stroll in the central plaza in the northern Mexican city of Guadalupe when presumed drug traffickers hurled grenades into the crowd. At least 14 people, more than half of them children, were injured, authorities said Sunday.

The assailants in the attack Saturday rode in two SUVs and quickly escaped the plaza. Several witnesses told Milenio television that local police blocked traffic after the explosion to clear the way for the attackers.

Mayor Ivonne Alvarez said she could not confirm that municipal police worked as accomplices but agreed to investigate "irregularities" with state authorities.

It was the second time in nearly four years of the drug war that presumed drug gangs used grenades against civilians in an open town square.

The first incident was freighted with political significance. It occurred two years ago in President Felipe Calderon's hometown, Morelia, on the night Mexico celebrates its independence. Eight people were killed in that attack and more than 100 wounded.

Calderon's government Sunday issued a statement strongly condemning the blasts in Guadalupe and calling on city, state and national agencies to stand up to "the threat represented by organized crime."

Guadalupe is a suburb of Monterrey, Mexico's affluent but increasingly violent industrial capital. The explosives detonated in the Guadalupe town square outside the Our Lady of Guadalupe Catholic Church and City Hall. The plaza was still decorated with "Viva Mexico" decorations from last month's bicentennial celebrations.

City Hall may have been the intended target. Five mayors were killed in a six-week period in August and September, including two in the Monterrey area. In one incident, local police were arrested in connection with the mayor's death.

Genaro Garcia Luna, the country's top security official, said recently that traffickers allot nearly $100 million a month to buy off municipal cops. He advocates replacing local police with state agencies reporting to a single national command.

The injured in Guadalupe included eight children, authorities said, the youngest age 2. None of the injuries was considered life-threatening.

About 24 hours earlier, grenades exploded at three locations in Monterrey — near a Justice Ministry building, the U.S. Consulate and a television station. One guard was reported injured at the ministry building, and damage was minimal. U.S. Consulate employees in Monterrey were ordered last month to send their children back to the United States because of mounting violence.

Elsewhere in Mexico, gunmen early Sunday opened fire on the offices of the Debate daily newspaper in the coastal city of Mazatlan, employees reported. There were no injuries. It was the fourth gun or grenade attack on newspapers in Sinaloa state, headquarters of the powerful Sinaloa cartel, in recent months.

And in the tourist mecca of Acapulco, army and navy forces joined in a widening search for 20 men kidnapped earlier in the weekend by armed gangs.

The men, described by friends as tourists from the neighboring state of Michoacan, were seized shortly after they arrived in Acapulco and were looking for a hotel. State officials said, however, there were inconsistencies in the men's information and details that did not check out.