MEXICO CITY — A shootout between police and suspected cartel hit men in central Mexico Friday left at least 12 people dead and one police officer wounded, officials said.

Guanajuato state Attorney General Carlos Zamarripa said police and soldiers were checking a report of armed men at a building in the town of Apaseo el Alto when assailants opened fire and lobbed grenades at them.

All the 12 dead were gunmen, Zamarripa said. Twelve suspects were detained.

Gov. Juan Manuel Oliva said one police officer was wounded in the shootout in Guanajuato.

The group was allegedly working for the Zetas, a gang of assassins tied to the Gulf cartel.

Mexico is suffering a wave of gang violence that has killed more than 10,800 people since President Felipe Calderon took office in December 2006 and launched a military-led crackdown on drug traffickers.

In the northern state of Sonora, assailants opened fire on a car carrying a congressional candidate for Calderon’s National Action Party, or PAN, killing two people who were with the candidate, party officials said Friday.

Ernesto Cornejo Valenzuela, who was unharmed, was campaigning in the town of Benito Juarez late Thursday when he was attacked, said Julio Cesar Frias, the party’s spokesman in Sonora, across the border from Arizona.

The federal Attorney General’s office said in a statement that gunmen in a pickup truck fired R15 and AK-47 rifles at the candidate’s car.

The PAN has concentrated its campaign for the July 5 midterm congressional elections on pushing forward Calderon’s fight against organized crime.

Frias said investigators had not established a motive for the attack.