I am curious just how credible this high-ranking official source is. These are pretty explosive claims and if true, have the potential to jeopardise US > Germany relations and force other countries including Australia and New Zealand to investigate and question if the US has been doing the same elsewhere.

If this is seriously true, then the US are most definitely spying on everyone. This is the kind of stuff that starts wars, it's actually quite scary what the NSA has been and continues to do.