Intelligence agencies, navies and air forces from at least 13 nations are quietly co-operating in a “secret war” against Pyongyang and Tehran.

It has so far involved interceptions of North Korean ships at sea, US agents prowling the waterfronts in Taiwan, multinational naval and air surveillance missions out of Singapore, investigators poring over the books of dubious banks in the former Portuguese colony of Macau and a fleet of planes and ships eavesdropping on the “hermit kingdom” in the waters north of Japan.

Few details filter out from western officials about the programme, which has operated since 2003, or about the American financial sanctions that accompany it.

But together they have tightened a noose around Kim Jong-il’s bankrupt, hungry nation.

“Diplomacy alone has not worked, military action is not on the table and so you’ll see a persistent increase in this kind of pressure,” said a senior western official.

In a telling example of the programme’s success, two Bush administration officials indicated last year that it had blocked North Korea from obtaining equipment used to make missile propellant.

The Americans also persuaded China to stop the sale of chemicals for North Korea’s nuclear weapons scientists. And a shipload of “precursor chemicals” for weapons was seized in Taiwan before it could reach a North Korean port.

According to John Bolton, the US ambassador to the United Nations and the man who originally devised the programme, it has made a serious dent in North Korea’s revenues from ballistic missile sales.

But the success of Bolton’s brainchild, the Proliferation Security Initiative (PSI), whose stated aim is to stop the traffic in weapons of mass destruction, might also push North Korea into extreme reactions.

Britain is a core member of the initiative, which was announced by President George W Bush in Krakow, Poland, on May 31, 2003. British officials have since joined meetings of “operational experts” in Australia, Europe and the US, while the Royal Navy has contributed ships to PSI exercises. The participants include Australia, New Zealand, Japan, Italy, Spain and Singapore, among others.

There has been almost no public debate in the countries committed to military involvement. A report for the US Congress said it had “no international secretariat, no offices in federal agencies established to support it, no database or reports of successes and failures and no established funding”.

To Bolton and senior British officials, those vague qualities make it politically attractive.

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