Airspace above Havre airport in Montana was briefly closed this evening after a fourth unidentified flying object was spotted, it has been reported.
The Federal Aviation Authority briefly closed the airspace just four hours after US fighter jets shot a 'small cylindrical object' out of the sky above Canada.
Montana Congressman Matt Rosendale said the airspace had been closed due to an “object that could interfere with commercial air traffic".
The North American Aerospace Defense Command later issued a statement saying airspace had been shut due to a “radar anomaly” that required fighter aircraft “to investigate".
“Those aircraft did not identify any object to correlate to the radar hits,” NORAD said.
Charming UK village is 'UFO hotspot' with 'NASA scientists showing interest'It added that it would continue to monitor the situation as it unfolds.
It comes after Canada shot down an 'unidentified object' after it entered its airspace, the country's prime minister has said.
This, in turn, follows one day after the US president ordered a fighter jet to shoot down an unidentified "high-altitude object" off Alaska.
In a tweet, Justin Trudeau wrote: “I ordered the take down of an unidentified object that violated Canadian airspace. @NORADCommand shot down the object over the Yukon.
"Canadian and U.S. aircraft were scrambled, and a U.S. F-22 successfully fired at the object."
It is not clear what the object was or if it was related to the Chinese spy balloon shot down last week or the other object that was shot down on Friday.
The object that was downed on Friday was flying at 40,000ft over the coast of Alaska and had reached speeds of 40mph - it was travelling towards the North Pole before being intercepted.
The White House said the object was "the size of a small car" and posed a "reasonable threat" to commercial flights. The purpose of the object remains unclear.