Venezuelan President Nicolas Maduro (C), his wife Cilia Flores (L) and military authorities reacting to a loud bang during a military ceremony.
Maduro, who was reelected in May in a vote that dozens of foreign governments described as rigged, is preparing to remove five zeroes from the country's currency in an effort to keep up with inflation. Because drones can be remotely operated, people may just use them to attack unsuspecting victims.
The alleged attack involved two drones, each carrying a kilogram (2.2 pounds) of the plastic explosive C4, which Reverol said on state television is "capable of causing effective damage over a 50-meter (164-foot) radius".
Interior Minister Néstor Luis Reverol said six "terrorists" had been detained Sunday, the Associated Press reported. "In the next hours there could be more arrests". He said one took part in 2014 anti-governments protests that rocked Venezuela's as it descended deeper into an economic crisis that is now worse than the Great Depression. The other had a warrant out for his arrest for participating in an attack on a military barracks.
Maduro initially blamed outgoing Colombian President Juan Manuel Santos and residents of the US state of Florida for the attack.
A second drone "lost control in the general area of the event and struck a building known as Don Eduardo near Bolivar Avenue, detonating at the height of the first floor as it fell to earth", Reverol said.
"We were doing videos from our auto because it was raining and then we tried to go near Bolivar Avenue to show the situation when national guard and military intelligence approached us, " Neidy Freites, a reporter for the live-streaming news site VivoPlay said in a video posted on the outlet's Twitter account.
The people on stage looked up, startled as the explosion was heard. "It was so strong the building shook", she said "I said, 'Oh my God, what happened.' It terrified me".
In an address to the nation Saturday night, a visibly shaken Maduro recalled seeing a "flying device" that exploded.
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Colombia also rejected Maduro's "absurd" accusation of involvement. Bodyguards escorted him from the event, covering him in black shields, and TV footage showed uniformed soldiers break formation and scatter.
There has been an attempt to assassinate me.
The march in support of the president was convened by the ruling United Socialist Party of Venezuela (PSUV) and will depart from the center of Caracas to end at the Miraflores government palace, where Maduro will give a speech. "Colombian President Juan Manuel Santos is behind this attack". The group has said that its goal is to unite Venezuela's resistance groups, and they released a statement late Saturday in which they decried the state of the country under Maduro.
Colombian authorities hitback calling the claims "baseless" and USA national security advisor John Bolton insisted there was "no United States government involvement" before suggesting that the incident could have been "a pretext set up by the regime itself".
A little-known group calling itself Soldiers in T-shirts claimed responsibility for the attack, the AP reported.
Maduro was speaking at a military parade to honor the National Guard, a body the opposition accuses of being primarily responsible for the 125 deaths during four months of civil unrest in 2017.
Last year, a rogue Venezuelan police officer hijacked a helicopter and fired at government buildings in what he said was an action against a dictator.
David Smilde, a senior fellow at the Washington Office on Latin America, said the "amateurish" attack made Mr Maduro appear vulnerable and did not appear to be a staged for political gain.