Invading extra-terrestrials, weather balloons or spy satellites - what exactly are the "unidentified flying objects" shot down over the United States and Canada?
The first was downed in the Atlantic Ocean, off the coast of South Carolina, on February 4 by the US military. China insisted it was one of their weather balloons which had gone adrift but it sparked concern after flying over nuclear bases as well as a US Air Force Base in Montana.
Three further as-yet-unidentified objects have been shot down. Two in US airspace - one on Saturday over North Alaska, one over Lake Huron in Michigan on Sunday, and a third over Canada’s Central Yukon territory on Saturday.
