The American ships are doing UN-approved duty. Resolution 1874, passed unanimously by the Security Council on June 12th permits the searching of North Korean cargoes on vessels on the high seas suspected of carrying illegal arms shipments. But, in what seems a nose-thumbers' charter, it requires the flag-owner's consent, which in this case is highly unlikely to be forthcoming. If the Americans cannot direct the Kang Nam 1 with stern words to a nearby port for a search, they will have to hope a shortage of fuel forces it to dock.

The new restrictions on North Korea limit its weapons imports to small arms, and ban all arms exports, conventional or otherwise. They followed a provocative long-range missile test and last month a defiant claim of the country's second nuclear test. Puzzlingly, sensors failed to detect telltale gases that usually leak out within days of such a test, but that could be because North Korea is, troublingly, better at testing small nuclear warheads deep underground than observers had guessed.

The regime's ailing boss, Kim Jong Il, is preparing more fireworks: perhaps another nuclear test; almost certainly short- and medium-range missile firings. A new launch-pad being prepared in the west of the country would allow testing of intercontinental-range rockets to the south, instead of as now across the Pacific towards America, which has threatened to shoot down any that appear threatening.

Where will all this lead? China and Russia, angered at Mr Kim's nuclear antics, agreed to support sanctions on his illicit weapons trade, but want six-party negotiations that also include America, South Korea and Japan, as well as North Korea, to resume. North Korea says it will come to the table as a "proud nuclear power" with no intention of giving up its bombs. "Delusional" is how one senior American official describes Mr Kim's demand to be accepted as a nuclear power; South Korea and Japan concur.

Meanwhile the fear is that Mr Kim will resume (if he ever stopped) helping others with their nuclear work. Financial records show that Mr Kim co-operated with a network run by a disgraced former Pakistani scientist, Abdul Qadeer Khan, to help supply Libya with nuclear material for uranium-enrichment work before the country abandoned its weapons effort. A nuclear reactor Mr Kim was secretly building for Syria, one ideally sized for producing plutonium for bombs, was destroyed by Israel in 2007 just before its completion.

Some reports say the Kang Nam 1 is carrying missile parts; others that it is shipping mostly small arms to the junta in Myanmar. Mr Kim has sometimes used Myanmar to trans-ship missile parts, and who knows what else, to Iran. But Myanmar itself is a headache now, too. Russia has agreed to build it a small nuclear-research reactor. The worry is this nuclear toing and froing could disguise another joint venture, with North Korea: the secret building of a reactor like both Syria's and the one Mr Kim has used to produce plutonium for his own weapons tests.

© The Economist Newspaper Limited 2009