At least 19 people have been killed in clashes involving armed men and security forces in the gang-plagued northwestern Mexican state of Sinaloa, authorities said.
Sinaloa has seen a dramatic increase in homicides following the capture and extradition of convicted drug lord Joaquin "El Chapo" Guzman.
The violence began with a shooting on Friday that killed two men near a department store in the town of Villa Union, about 24km southeast of the beach resort of Mazatlan.
Officials attributed it to warring drug gang members responsible for recent violence in the state, which is home to Guzman's Sinaloa cartel.
"We believe it has to do with the transport of drugs and the fight for terrain, for the areas that these groups are fighting over," Genaro Robles Casillas, the Sinaloa state public security secretary, said at a news conference.
Police were alerted by emergency calls, and municipal officers encountered the suspected attackers as they were riding in several pickup trucks.
A fierce gun battle broke out in which police killed 17 suspects, officials said. Five municipal police officers were wounded, but reported in stable condition.
At the scene of the clash, four vehicles, 15 rifles and seven handguns were found.
Sinaloa is the birthplace of a number of Mexico's drug gang leaders, and killings have risen there after Guzman was captured and then extradited to the United States earlier this year to face drug charges.
Security experts say a power struggle has since broken out between opposing factions of the Sinaloa cartel, which also faces challenges from other gangs such as the Jalisco New Generation cartel.
During the first five months of the year, homicides jumped by 76 percent in Sinaloa state compared with the same period in 2016, according to government crime statistics.
The killings include the May 15 slaying of Javier Valdez, an award-winning reporter who specialised in covering drug trafficking and organised crime, in the state capital, Culiacan.
Source: News agencies