The video did not say whether the authorities had verified the existence of a conspiracy.

Blu Radio reported that the Venezuelans, who were arrested in the cities of Valledupar and Barranquilla this month, had in their possession an assault rifle with a telescopic scope, as well as an Uzi, ammunition and stun grenade.

Blu, citing unidentified sources, said any plot would have likely had the support of armed Colombian leftist rebels or drug-trafficking organizations, and would have been timed to coincide next month with the start of the second term of President Nicolas Maduro of Venezuela.

There was no immediate reaction from Venezuela’s government.

In his video, Mr. Holmes appealed to Colombians to share any information that could affect the president’s safety. He expressed appreciation for the cooperation of unidentified foreign intelligence agencies for helping to protect the Colombian president.

Mr. Duque, 42, who took office in August, has been leading a diplomatic effort in Latin America to isolate Venezuela’s socialist government as Mr. Maduro looks set to cement his hold on power amid a devastating economic crisis that has spurred millions of Venezuelans to flee to neighboring countries to escape widespread food and medicine shortages and hyperinflation.