Washington (CNN) -- The U.S. State Department on Thursday extended a travel warning that had been issued for Mexico because of the region's high level of drug and gang violence. The State Department warning also notes that the authorized departure of family members of U.S. government personnel from U.S. consulates in the northern Mexico border cities of Tijuana, Nogales, Ciudad Juarez, Nuevo Laredo, Monterrey and Matamoros has been extended. The State Department issued similar warnings in March and April. The Mexican government said in April that more than 22,700 people have been killed in drug-related violence since December 2006, when...