Bluster or legitimate threat, U.S. President Donald Trump's latest castigation of North Korea has again left observers wondering if the leader will greenlight some kind of military action against the country in a bid to halt its seemingly inexorable march toward a credible nuclear strike capability.

Trump on Saturday issued his latest veiled threat to Pyongyang in a series of tweets deriding past U.S. leaders' attempts to solve the intractable North Korean nuclear issue, saying that "only one thing" could bring the crisis to a close — an apparent allusion to military action.

"Presidents and their administrations have been talking to North Korea for 25 years, agreements made and massive amounts of money paid," Trump tweeted. "Hasn't worked, agreements violated before the ink was dry, makings fools of U.S. negotiators. Sorry, but only one thing will work!"