A highway bomb attack in southwestern Colombia has killed 19 people and injured at least 38, the latest spate of violence ahead of next month’s presidential election.

Buses and vans were left mangled in the blast Saturday on the Pan-American Highway, in the restive southwestern Cauca department.

Several cars were flipped over by the force of the explosion and a large crater was blown out of the roadway.

The department’s governor on Saturday evening provided a death toll of 14, with more than 38 injured, but the National Institute of Legal Medicine and Forensic Sciences said Sunday morning it had begun the examination of 19 bodies.

Military chief Hugo Lopez told a news conference on Saturday that the bomb had exploded after assailants stopped traffic by blocking the road with a bus and another vehicle.

The attack comes just over one month ahead of national elections, in which voters will pick a successor to President Gustavo Petro.

Petro blamed the bombing on Ivan Mordisco, the South American country’s most-wanted criminal, whom the president has compared to late cocaine kingpin Pablo Escobar.

The violence came after a bomb attack on Friday on a military base in Cali, Colombia’s third-largest city, injured two people and set off a string of attacks in the Valle del Cauca and Cauca departments.

According to Lopez, 26 attacks have been recorded in the two departments over the past two days.

Authorities have boosted military and police presence in the areas, Defence Minister Pedro Sanchez said.

Security is one of the central issues of the May 31 presidential election. Political violence was brought into sharp focus last June, when young conservative presidential frontrunner Miguel Uribe Turbay was shot in broad daylight while campaigning in the capital Bogota and later died from his wounds.

Leftist Senator Ivan Cepeda, an architect of Petro’s controversial policy of negotiating with armed groups, is ahead in polls.

He is trailed by right-wing candidates Abelardo de la Espriella and Paloma Valencia, both of whom have pledged to take a hard line against rebel groups.

All three have reported receiving death threats and are campaigning under heavy security.