Multiple people who had allegedly been plotting a violent attack over the Halloween weekend were arrested Friday in Michigan, FBI Director Kash Patel said in a social media post.

The law enforcement effort was focused on suburban Detroit. Patel said more information would be released later.

Investigators believe the plot was inspired by Islamic State extremism and are investigating whether those in custody were potentially radicalised online, according to two people briefed on the investigation who could not publicly discuss details. They spoke on condition of anonymity.

FBI and state police vehicles were in a neighbourhood near Fordson High School in Dearborn. People wearing shirts marked FBI walked in and out of a house, including one person who collected paper bags and other items from an evidence truck.

Police in Inkster, another suburb, said FBI personnel were at a storage facility there.

“There is no current threat to public safety,” said Jordan Hall, an FBI spokesman in Detroit, who declined further comment.