The potential of harming civilians on the ground if it was shot down over land, conversely, was "moderate to significant".Officials also defended the timing of the balloon"s destruction, saying that doing so over rough terrain in Alaska or the cold waters of the Northern Pacific would have made recovery efforts difficult and dangerous.At a Wednesday news conference, Defence Department spokesman Brigadier General Pat Ryder confirmed that the US believed similar balloons had operated over North and South America, South East Asia, East Asia and Europe.