CIUDAD JUÁREZ, Mexico — Five men shot dead in a barbershop, their bodies slumped near the doorway. A decapitated body dumped next to a housing development. Three others killed behind a pool hall and several more in a bar called Tres Mentiras, or Three Lies.

By the end of October, at least 96 people had been killed in the border city of Ciudad Juárez. It was the highest monthly tally since 2012, sowing fears of a return to the gangland mayhem that once earned this city the title of the most violent place in the world.

Back then, the bloodshed in this city was in a class of its own. But now it has company, with other Mexican cities that are as bad or worse. In the last year, the number of homicides around Mexico has soared to levels not seen in several years.

In the first 10 months of this year, there were 17,063 homicide cases in Mexico, already more than last year’s total and the highest 10-month tally since 2012. The relapse in security has unnerved Mexico and led many to wonder whether the country is on the brink of a bloody, all-out war between criminal groups.