What we know about the mysterious flying objects downed by the US

The Pentagon said none of the four objects appeared armed or posed any threat of attack [File: Patrick Semansky/AP Photo]

The downing of a huge Chinese balloon off the US coast, followed by the shootdowns of three smaller objects over Alaska, Canada and Lake Huron on the US-Canada border, has raised concerns about North American security and further strained relations with China.

Here is what we know so far: