The US says it is not surprised by Putin's announcement, and that its military is ready to defend the nation no matter what.

DANA WHITE PENTAGON SPOKESPERSON "We're not surprised by the statements and the American people should rest assured that we are fully prepared. Again, we are not surprised by his statement. Our stance has never been, they know very well it is not about them. Our missile defense has never been about them. We need to ensure we have a credible nuclear deterrent and we are confident that we are prepared to do, and we are prepared to defend this nation no matter what."