The FBI believes authorities disrupted a terrorist attack that was being planned in a small western Minnesota city after converging on a mobile home that contained Molotov cocktails, suspected pipe bombs and firearms.
Buford Rogers, 24, was arrested at the weekend and charged with one count of being a felon in possession of a firearm. He has made his first court appearance and a federal defender was appointed for him, but an attorney was not immediately assigned to his case.
"The FBI believed there was a terror attack in its planning stages, and we believe there would have been a localized terror attack, and that's why law enforcement moved quickly to execute the search warrant on Friday to arrest Mr Rogers," FBI spokesman Kyle Loven said Monday.
Rogers appeared in court wearing a construction company T-shirt, jeans and work boots. He answered "yes sir" and "no sir" to questions from US Magistrate Tony Leung.
Leung ordered Rogers held pending a detention hearing, citing "serious concerns" raised in the criminal complaint.
Loven declined to elaborate about the location of the alleged target, other than to say it was believed to be in Montevideo, a city of about 5,000 people about 209 kilometres west of Minneapolis.
He also declined to say whether Rogers was believed to be acting alone or as part of a group, or if other arrests were expected.
"This is a very active investigation," he said. He added that at this point, authorities are "looking at this from a domestic terrorism standpoint."
Loven said the pending investigation prohibits him from getting into details about Rogers' possible political or religious views, but he said the FBI is confident in calling this a "terror" situation.
"We had information which indicated that Mr Rogers was involved in a plot to conduct terror activities in and around the Montevideo area," he said.
In a news release, the FBI said it believed "the lives of several local residents were potentially saved" by the search and arrest, and said "several guns and explosive devices were discovered."
The agency said the alleged terror plot was discovered through analysis of intelligence gathered by local, state and federal authorities.
According to a federal affidavit obtained by The Associated Press, FBI agents from the domestic terrorism squad searched the property at the mobile home park in Montevideo and discovered the Molotov cocktails, suspected pipe bombs and firearms.
The affidavit said Buford was there at the time of the search, and one firearm recovered from Buford's residence was a Romanian AKM assault rifle.
In an interview with authorities, Rogers admitted firing the weapon on two separate occasions at a gun range, the affidavit said. Rogers has a 2011 conviction for felony burglary and is not allowed to have a firearm.
Rogers is expected to make his initial appearance in federal court today.
Rogers also has a 2009 misdemeanour conviction for dangerous handling of a weapon, as well as other criminal violations, according to online court records.