Local media had earlier reported Villavicencio, a former lawmaker who had been polling at 7.5% voting intention, had been shot at a campaign event in Quito.
“For his memory and his fight, I assure you that this crime will not remain unpunished,” Lasso said on X, the social media platform formerly known as Twitter. “Organized crime have gone very far, but all the weight of the law will fall on them.”
Lasso said he would host top security officials at an urgent meeting.
Videos on social media purportedly from the campaign event showed people taking cover and screaming as gunfire sounded.