The FBI thwarted a plot targeting Sunday's UFC event at the White House, and has taken multiple suspects into custody, according to the agency's head, Kash Patel.
Part of the plan involved striking nearby buildings with explosive-laden drones, according to court documents unsealed on Tuesday.
One suspect was arrested in Ohio last week, where investigators obtained access to encrypted messages involving other alleged plotters. He has been charged with conspiracy to commit an offence against the US and attempted murder of a federal officer, according to the documents.
"Allegedly planned attacks were stopped cold," Patel said in a social media post on Tuesday about the "multi-state operation".
Five people are in custody, CBS News, the BBC's US news partner, reported. The BBC has requested further comment from the FBI.
By using the drones, the plotters aimed to spark panic and draw the fleeing crowd toward a sniper team, according to the court documents.. A "second wave" of attackers then allegedly was supposed to storm the White House gate.
An estimated 4,300 people were present for the invite-only event on the South Lawn - and another 85,000 were able to watch at a nearby fan zone - as 14 mixed martial arts fighters competed in back-to-back fights on Sunday,
The plot was discovered through Tycen Proper, a 19-year-old Ohio man, who was communicating with a group online who "expressed ultra-religious and antigovernment sentiments," federal prosecutors said in the unsealed charges.
His mother called local authorities late in the evening on 10 June - just days before the high-profile event - because she was concerned about his large firearms purchases and what she had seen of his online communication with a group that claimed to be made up of former military members and Christian-based.
The group allegedly wanted to "jumpstart" a revolution by shooting at "high-value targets" - identified as wealthy people and politicians - attending the fight, and had specifically discussed "grievances about government corruption, the handling of the Epstein files, data centers taking up all the water in communities, and other government actions", according to court documents.
During an FBI interview on 11 June, Proper admitted to being part of planning the coordinated attack and that the group began communicating with one another around March 2026 through a TikTok group called "Vanguard of the Old".
For some in the group, those communications moved to Signal, the encrypted messaging app, where plans for the attack on the White House event were made, according to prosecutors.
The BBC has contacted Proper's lawyer.
At an unrelated briefing on Tuesday, Secret Service Deputy Director Matt Quinn was asked about the thwarted incident and described it as a "serious threat".
He told reporters he could not offer many details as the investigation remains active, but said "there are still suspects at large, and we're going to work it until everyone's been identified".
The Secret Service worked "closely with the FBI throughout this investigation," and their "formal comments regarding the specifics of this case will be made available in court filings", Secret Service Director Sean Curran said in a statement.
It appears President Donald Trump and Vice President JD Vance were made aware of the possibly thwarted attack around the same time as the general public.
When asked about the alleged plot during the G7 summit in France on Tuesday Trump said: "I haven't heard about it."
While Vance said in an interview on Fox News "Fox and Friends" that he believed the FBI was informing the public "because the scale of the planned attack is so significant".
On Sunday, as part of the celebration of the nation's 250th anniversary, the White House hosted a series of Ultimate Fighting Championship (UFC) matches, after days of preparation that included erecting a massive arena known as The Claw in the open space behind the White House and other events such as a ceremonial weigh-in of the fighters.
The event coincided with Trump's 80th birthday. Some members of his administration were in attendance, as were some celebrities.
The alleged plot comes some two months after a shooting at the White House Correspondents dinner, where Trump was in attendance and one month after a man was killed by Secret Service agents after opening fire at White House checkpoint.
In newly unsealed court filings, the government says the group allegedly expressed grievances about corruption, the Epstein files, and data centres.
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