Washington: What to do about North Korea and its weapons program? North Korean dictator Kim Jong-un has seemingly crossed a threshold - he now has missiles that go halfway around the world, despite a January warning, when then president-elect Donald Trump declared: "It won't happen!"

If Trump's tweet was an implicit threat of a pre-emptive strike by Washington, it stands out in the administration's menu of possible responses as the only one that has not been attempted.

All the others - containment, sanctions, negotiations and cyberwar - have been tried in various configurations by previous administrations, to little effect.

The test seems to prove that Pyongyang now has a genuine intercontinental ballistic missile - confirming that it's capable of striking Alaska. And given the pace of the advances in North Korea's weapons expertise, experts warn that in time it will figure out how to arm the new missile with a nuclear warhead.

That the North already had the capability to strike South Korea and Japan, possibly with nuclear-armed missiles, had a certain abstract quality for Washington. With Alaska now in Pyongyang's crosshairs the calculus changes dramatically - but useful responses remain elusive.

As Americans celebrated Independence Day on Tuesday, Kim taunted Trump, describing the test as a milestone in his plans to bring the US within strike range and as a Fourth of July "gift" to the administration.

"We should send them gifts once in a while to help break their boredom," he was quoted as saying in a report by the state-run news agency.

In keeping with the US administration's refusal to be specific about likely responses, it warned on Tuesday it would use "the full range of capabilities at our disposal against the growing threat".

And in a joint exercise with South Korea, it flexed its own muscles, firing missiles in war games off the Korean Peninsula.

The sentiments in Trump's tweets following the missile launch were in the same vein as Kim's blather.

"North Korea has just launched another missile. Does this guy have anything better to do with his life?" Trump asked.

"Hard to believe that South Korea and Japan will put up with this much longer. Perhaps China will put a heavy move on North Korea and end this nonsense once and for all!"

But just as Pyongyang seems impervious to all that Washington has tried to date, so too, it seems, is Beijing.

Chinese President Xi Jinping was unmoved by a folksy dinner with Trump at Mar-a-Lago and by a subsequent presidential Twitter spray, as it dawned on Trump that China was playing to its own regional agenda, not Washington's.

Now Trump has told Beijing that Washington will go it alone in confronting Pyongyang - without saying what that means.

Writing jointly in 2006 with former Obama defence secretary Ash Carter, former Clinton administration defence chief William Perry advocated a pre-emptive strike - but he no longer thinks it a viable option, because the missile capability developed by the North in the intervening years could wreak appalling destruction on Seoul, the South Korean capital.

Despite past failures, newly elected South Korean President Moon Jae-in pushed for renewed negotiations with the North in a meeting with Trump in Washington last week.

Moon is proposing essentially what Beijing and Moscow are pushing - a diplomatic engagement in which the North would be asked to freeze its nuclear and missile tests and for the US to agree to reduce or end military exercises with the South.

Washington is wary. Such a deal would acknowledge the reality that Pyongyang is a nuclear power - albeit with just a dozen or more nuclear weapons - and militarily and strategically, it would put the US in a straitjacket in the Pacific. But the Trump administration reportedly is responsive to the notion of a freeze being a scene-setter to the North surrendering its nuclear program in an ultimate deal for a nuclear-free Korean Peninsula.

The contours of Trump's "go it alone" strategy are becoming apparent - selling weapons to Taiwan, sanctions on a small group of Chinese banks and individuals who do business with the North, challenging China's territorial claims, citing China as a worst-offender in the State Department's annual report on human trafficking and renewed warning of action against China for dumping steel in the international market.

The risk in all this is that, instead of resolving the existing North Korea crisis, it will only create a new crisis with Beijing. China experts say that Xi is eager to continue dialogue with Washington, but if Trump extends the limited sanctions on Chinese businesses dealing with North Korea, Beijing is likely to retaliate.

China has applied limited sanctions to North Korea, acting earlier this year to reduce its coal imports from the North. But it is not prepared, yet, to accept the collapse of the regime and the ensuing chaos on its doorstep, in which the US most likely would emerge as a major military force on the peninsula. As much as Beijing opposes the rise of a nuclear North, the North-South stalemate suits its regional game plans.