A British air base used by the U.S. Air Force was scouted out in 2015 by an Islamic extremist who eventually received a life sentence for plotting an attack against U.S. military personnel.

Junead Khan was tried for using his job as a delivery driver to study RAF Mildenhall, the base in England that was locked down on Monday during a disturbance that resulted in a man's arrest.

Authorities have not said if the incident at Mildenhall was suspected to be terror-related. Details have not yet been released.

A jury convicted Khan last year of planning to travel to Syria as a support of the Islamic State group and preparing possible attacks at Mildenhall and a second English base, RAF Lakenheath.

U.S. Air Force Europe says there are reports of a security incident at British air base used by the U.S. Air Force and that the situation is ongoing.

The U.S. has air-refueling assets stationed at RAF Mildenhall in Suffolk, England, located 80 miles north of London.

The Royal Air Force base says it was locked down after reports of a disturbance at 1 p.m. Monday.

It says emergency personnel are responding to the situation and that additional details would be provide when possible.

British media are suggesting someone in a vehicle tried to force his way through a checkpoint, but this hasn't been confirmed.

British police say they are responding to a "significant" incident at a Royal Air Force base used by the U.S. Air Force.

Police say it happened at RAF Mildenhall in Suffolk and urged the public to stay away from the area for the time being. Police said Monday that further details would be released shortly.

British media suggested an individual in a vehicle tried to force his way through a checkpoint, but this wasn't confirmed.

RAF officials referred calls to police.