FILE PHOTO - A federal police officer stands behind a police tape near a crime scene in Apodaca on the outskirts of Monterrey February 26, 2012. REUTERS/Daniel Becerril

MEXICO CITY (Reuters) - The number of murder investigations in Mexico rose to a record high in May, official data showed, as criminal violence increased dramatically since last year.

There were 2,186 murder probes in May, the highest for any month in data going back to 1997, according to the latest government statistics.

Some cases may include multiple homicides, and the number of murder victims reported in May was 2,452, the highest for any month in a separate series of data that only goes back to 2014.

The violence has contributed to a slump in the popularity of President Enrique Pena Nieto, and could undermine support for his Institutional Revolutionary Party in next year’s presidential race. Mexican presidents can only serve one six-year term.

Murder investigations in the first five months of the year totaled 9,916 cases, up nearly 30 percent from the same period in 2016.

Discoveries of bodies tossed by the roadside, strung up on bridges as warnings to rival drug gangs, or buried in mass graves have become almost daily events in Mexico.

The capture or killing of major drug bosses during the past decade led to an increase in the number of gangs fighting each other over turf and battling government forces.

According to statistics from the U.N. Office on Drugs and Crime, Mexico’s murder rate in 2015 was 16.35 people per 100,000, sharply higher than the U.S. rate of 4.88 per 100,000 people, but much lower than in many countries in Central America and the Caribbean.