BOGOTÁ (AFP) — Colombia marked a national day of mourning Monday after a roadside bomb killed 21 people in southwestern Cauca province, the country’s deadliest attack on civilians in decades and a major escalation of pre-election violence.

The blast Saturday left a large crater and destroyed several vehicles, with AFP journalists reporting bodies and wreckage at the scene. It was the worst single attack since a 2003 Bogota nightclub bombing that killed 36 people.

Hundreds attended a vigil in Cajibio, where many of the victims were from a nearby village, wearing white and calling for peace.

“Please, no more death, no more violence,” said Joao Valencia, 42, a relative of a victim.

The government of President Gustavo Petro blamed the Central General Command guerrilla group, led by Ivan Mordisco, which operates in the coca-growing region and has previously engaged in peace talks.

Defense Minister Pedro Sanchez said the violence reflects pressure from security operations. “Terrorism…is because the pressure is so intense...that the only option is to attack the most defenseless,” he said.

Officials reported at least 31 guerrilla attacks across southwest Colombia since Friday, as violence intensifies ahead of the 31 May presidential election.

The attack has sharpened debate over Petro’s “total peace” policy, with critics calling for a harder security response and supporters warning of a “climate of fear” ahead of the vote.