At least six people were killed and more than 20 wounded when a hand grenade exploded outside a crowded bar before dawn on Saturday in the western city of Guadalajara, Mexican police said.
Around 4.00am (1000 GMT) an unknown assailant threw "a fragmentation grenade at the bar porch," local police told reporters.
Several men opened fire at the bar, which was packed with customers, then fled in several cars, police said.
The victims were three women and three men, police said.
Drug gangs have escalated a violent turf war in the past weeks in Guadalajara, the second most populous city in Mexico with 4.4 million residents.
This is the second grenade attack on a Guadalajara bar in less than a month: on January 16 an argument between armed men and a music band ended in a blast that killed two people.
More than 34,600 people have been killed in drug trafficking related violence since December 2006, when the government of President Felipe Calderon deployed soldiers and federal police in a widespread crackdown on the illegal cartels.