The U.S. military said late on Saturday a radar anomaly prompted the temporary closure of airspace to civilian airplanes in Montana but no threatening object was detected.
The North American Aerospace Defense Command (NORAD) sent fighter aircraft to investigate but the aircraft "did not identify any object to correlate to the radar hits. NORAD will continue to monitor the situation."
Earlier on Saturday, a U.S. F-22 fighter jet shot down an unidentified cylindrical object over Canada, the second such shootdown in as many days. Canada and the United States have been on heightened alert following an episode earlier this month where a Chinese high-altitude balloon the U.S. said was spying was tracked from Montana to South Carolina and then shot down off the coast.
The U.S. Federal Aviation Administration (FAA) earlier on Saturday closed and then reopened airspace in Montana after temporarily barring flights in an area about 50 by 50 nautical miles (93 by 93 km) around Havre, Montana, near the Canadian border.
The FAA issued similar flight restrictions in response to the earlier suspected Chinese spy balloon.
Three lawmakers said on Twitter there was an unidentified object seen in Montana airspace Saturday.
Representative Matt Rosendale, a Montana Republican, said on Twitter he was in contact with the U.S. military "and monitoring the latest issue over Havre and the northern border."
He said the issue was because of "an object that could interfere with commercial air traffic — the DOD will resume efforts to observe and ground the object in the morning."
Senator Jon Tester of Montana wrote on Twitter he was "aware of the object in Montana air space and remain in close contact with senior DOD and Administration officials."
(Reporting by David Shepardson, Idrees Ali and Phil Stewart, editing by Deepa Babington and Christian Schmollinger)