Six men suspected of involvement in the murder in August of Ecuador's anti-corruption presidential candidate Fernando Villavicencio were killed in prison on Friday, the prisons agency said, barely a week before a crucial run-off election.

The killings took place in a penitentiary in Guayaquil, the South American country's largest city, the attorney general's office announced earlier on Friday.

Ecuador's government swiftly condemned the killings.

Outgoing President Guillermo Lasso pledged "neither complicity nor cover-up" in getting to the bottom of the killings, in a post on social media platform X, formerly known as Twitter.

"Here the truth will be known," he said.

The SNAI prisons agency said in a statement the six men were all Colombian nationals. It gave no more details of the killings.

The government has said authorities are determined to identify those behind Villavicencio's murder.