Fighter jets were scrambled and Montana's airspace closed due to a 'radar anomaly', officials said on Saturday night - admitting that nothing suspicious was detected by the planes.

NORAD, the North American Aerospace Defense Command, issued a statement hours at 9:30pm on Saturday night - an hour after Montana congressman Matt Rosendale said jets were responding to an 'airborne object' spotted above his state.

NORAD said they 'detected a radar anomaly and sent fighter aircraft to investigate.'

They continued: 'Those aircraft did not identify any object to correlate to the radar hits.

'NORAD will continue to monitor the situation.' 

The Federal Aviation Authority briefly closed the airspace above Havre airport in Montana at 7.40pm EST citing 'national defense' amid reports of 'an object that could interfere with commercial air traffic'.

Data from FlightRadar.com showed a KC-135 Stratotanker - an American military aerial refueling aircraft - circling the area before airspace was reopened at around 8.20pm.   

Rosendale, a Republican congressman representing Montana who claimed to be in direct contact with NORCOM (Northern Command), said the Department of Defense would not shoot down the unidentified object until day broke on Sunday.

'I am in direct contact with NORCOM and monitoring the latest issue over Havre and the northern border,' Rosendale tweeted. 

'Airspace is closed due to an object that could interfere with commercial air traffic — the DOD will resume efforts to observe and ground the object in the morning.'

Havre, home to 10,000 people, is 30 miles south of the Canadian border.