Gunmen opened fire on people watching a soccer match in central Mexico, killing 11 and injuring 12 others.
The mayor of Salamanca, Cesar Prieto, said the attack happened near the end of the game when the gunmen entered the field and started shooting.
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Some of the injured are receiving treatment in hospitals, and no group has claimed responsibility for the attack.
Authorities said they suspect drug trafficking gangs may be behind the shooting, as violence has been rising in parts of the country.
Mexico is one of three countries hosting some matches of the World Cup, raising concerns about security.