The situation in the US does not seem so clear.
US Marshals Hold Much Less Than 200K BTC, FOIA Docs Reveal the Real NumberUS Marshals only hold 28,988 BTC instead of earlier estimates of over 200,000.
As for whether they are buying, it could be, but we have no official statement on the matter. So until they come out and make a public statement, we can't take it for granted.
Are we witnessing the start of a global Bitcoin arms race?
It could be starting, but we're not witnessing anything, I would say.