A 45-year-old US man was among five people killed in two bar shootings in Mexico's second biggest city, with a
grenade used in one of the attacks, authorities have said.
Officials said a total of 45 rounds were fired off with 9mm handguns in the attacks in the western city of Guadalajara late on Sunday, wounding another 17 people.
Witnesses said a single gunman opened fire outside the bar in each attack.
The shootings took place 15 minutes apart and appeared to be aimed at the owners of the bars, who are related, said senior prosecutor Jorge Villasenor on Monday.
He added that investigators suspect organised crime was involved "due to the type of weapon that was used."
"The attack was directed at these places, not at a specific person. This is the line of investigation that we are looking into," he said. The two bar owners are being questioned in order to determine a possible motive.
Two people, including the American, were killed when a gunman opened fire on the "Gol" bar where people had watched the Chivas-America football derby, prosecutors said.
The American was identified by a female companion as Jeff Lydell Comer. The other victim was a 20-year-old Mexican man. Both were customers at the bar.
Fifteen minutes earlier, a gunman attacked the "Ruta 66" bar in a different neighbourhood, firing shots and throwing a grenade.
A 28-year-old customer and a 30-year-old employee were found shot dead outside the bar while a 23-year-old waitress later died of her gunshot wounds.
The explosion injured an unspecified number of people.
The prosecutor's office said 17 people were wounded but did not specify how many in each attack.
Four other men were killed in other attacks on Sunday across Guadalajara, which has endured some of the drug-related violence that has left 70,000 people dead in Mexico since December 2006.