Venezuelan President Nicolás Maduro announced Monday that he believes Colombia to be responsible for Saturday’s drone assassination attempt.

In a tweet, Maduro said that Venezuelan officials are continuing the investigation and that he would be presenting “strong evidence” of Bogotá’s involvement.

Outgoing Colombian President Juan Manuel Santos, who left office on Tuesday, denied the allegations and stated he was “doing more important things” during the attack, according to Al Jazeera.

According to a report from AFP, officials in the Maduro regime claim that “ultra far-right” groups within Venezuela who are working with Colombian officials and an anonymous financier in Florida collaborated to carry out the attack.

Venezuela’s Attorney General Tarek William Saab stated on Monday that “several suspects were in custody” and that the Venezuelan police would “track down all those who conspire against public peace.”

At this time, Venezuelan officials have not released any evidence that links Colombia to the attack.

Colombia and Venezuela’s relationship has been tense since the beginning Venezuela’s meltdown began in 2016. More than 1 million Venezuelans fled the country and crossed the border into Colombia to seek better conditions, and more than 600,000 remain there today. The mass influx of economic refugees prompted Santos to ask the international community for aid. Although Santos is no longer in power, his successor, Ivan Duque, also wants to take a hard line approach to the Maduro regime.