'Radar anomaly' detected over Montana hours after Canada downing: US military

North American air defense "detected a radar anomaly and sent fighter aircraft to investigate.

Airspace was closed over part of the state of Montana on Saturday and a fighter jet was sent to investigate a "radar anomaly" but the plane did not find anything unusual in the sky, the US military said.

A US Air Force installation surrounded by farmland in central Montana. (AP)

North American air defense "detected a radar anomaly and sent fighter aircraft to investigate. Those aircraft did not identify any object to correlate to the radar hits," a statement from the North American Aerospace Defense Command and US Northern Command said.

Officials "will continue to monitor the situation," the statement added, only hours after a joint US-Canadian operation shot down an object over the Yukon territory in Canada.