MILWAUKEE (AP) — A vehicle smashed into a security gate at a Wisconsin Air National Guard unit and a security officer fired a gun, prompting a lockdown and leading to the arrest of three people.

The Guard says no one was injured in the security breach and shooting at the 128th Air Refueling Wing in Milwaukee County about 3 p.m. Sunday. The base, adjacent to Mitchell International Airport, had returned to normal operations by Sunday evening.

Guard officials haven't released details about damage at the base, the suspects or what motivated the breach.

The three are in custody of the Milwaukee County Sheriff's Department.

The 128th Air Refueling Wing provides aerial refueling support to Air Force, Navy and Marine Corps aircraft, as well as aircraft of allied nations.