We can't be on the brink of nuclear war. The most talked-about story in America at the moment is not the North Korean military threat but a basketball scandal in New Jersey.

Futhermore, President Obama was not huddled overnight in the White House Situation Room. He was raising cash in San Francisco for his party's re-election efforts.

So, America shows no sign of great alarm at the incendiary rhetoric coming from North Korea. So far US policy-makers are staying admirably calm.

Read: North Korean army 'given approval' to launch nuclear strike on US threats

Perhaps Kim Jong-un is just engaged in domestic politics, shoring up support among his own military leaders by sounding tough and antagonistic.

But Chuck Hagel, America's new and untested Defence Secretary, is right to call North Korea a clear and present danger to the US.

It's true that North Korea, by common consent among intelligence experts, cannot miniaturise a nuclear device and put it on a ballistic missile. Guam, Hawaii and Los Angeles are not in danger.

However, the possibility of a miscalculation between the opaque, militaristic regime in the North and a nervous government in the South is real.

US Secretary of Defence Chuck Hagel. Credit: Reuters

Read: David Cameron: Foolish to scrap Trident

A naval clash in the Yellow Sea or an incident along the demilitarised zone could quickly spiral out of control.

Remember that North Korea has already severed the phone hotlines between the two sides. So a clash could escalate before its cause is fully understood.

An attack on South Korea would immediately draw the United States into the conflict. Washington knows that Iran is watching the Korean Peninsula closely, calculating the costs of retaining its own nuclear programme.

North Korean leader Kim Jong-un. Credit: Reuters/KCNA

What is clear from all this is that America needs China. It needs Beijing to hold back Kim Jong-un. China is threatened by regional instability even more than the US.

US Secretary of State John Kerry travels to the area next week. He will need all his skills to contain the crisis and re-open a channel of communication with a nation ruled by a bizarre leader who has no experience and who seems interested only in provocation.