The FBI says it prevented a potential attack using guns and drones on last Sunday's UFC event attended by President Trump at the White House.
The agency has taken five people into custody, according to court documents. A teenager has been charged with attempted murder.
The plot involved using explosive-laden drones to strike the north side of the White House with the aim of funnelling attendees towards an exit where snipers planned to open fire on fleeing politicians and others, the FBI says in the court papers.
A criminal complaint filed in Ohio showed Tycen Proper, 19, had been charged with attempted murder, conspiracy to commit an offence against the United States, and firearm offences.
Authorities discovered the plot when the Proper's mother called local police in Ohio to report that her son had made several weapons purchases and was interacting with concerning people online.
Bureau chief Kash Patel said they became "aware of a potential threat to the UFC America 250 event" on 10 June.
He said "multiple individuals" were now in custody. His X post appeared with a screenshot reading: "FBI disrupts alleged explosive-drone plot targeting White House UFC event".
Donald Trump attended the event, which was staged without incident on his 80th birthday (14 June) to commemorate the 250th anniversary of US independence.
Vice president JD Vance said authorities were looking at a possible underground network.
He told Fox News: "23 people do not get to the point where they're going to commit a mass terror incident in Washington DC without some serious funding, without some serious coordination."
The complaint alleges that rifles - including one painted with the US flag - were found at his home, along with thousands of rounds of ammunition.
Proper had "begun interacting with a group online that was comprised of individuals who claimed to be ex-military and Christian-based", his mother told the FBI in an interview.
The affidavit claims an attack was being planned with a number of others who believe the US needs to be "torn down so that it could be rebuilt".
Proper admitted planning a "coordinated attack against the United States government during the UFC event", the document adds.
The group was allegedly planning to stage a "demonstration" on the north side of the White House before the drone strikes.
Targets discussed among the group are said to have included senators Marsha Blackburn, Jim Justice, and Shelley Moore Capito; and representatives Carol Miller and Riley Moore.
The group of "approximately 19 individuals" chatted on the Signal app and planned how to escape to a "safe house", according to the document.
Thousands of fans and top officials watched the fights, including secretary of state Marco Rubio and House Speaker Mike Johnson.
Meta CEO Mark Zuckerberg was also among the spectators, as was Polish President Karol Nawrocki and former football player Zlatan Ibrahimovic.
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The crowd repeatedly chanted, "USA! USA!" during the fighting when an American faced a foreign opponent and many of the winners thanked Mr Trump.
The seven-fight card culminated in a shock defeat for Spain's previously undefeated Ilia Topuria at the hands of popular US fighter Justin Gaethje.
(c) Sky News 2026: Teen charged over White House UFC show attack plot
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