Singapore: Western diplomats are alarmed at cooperation between Myanmar and North Korea but have not confirmed fears Pyongyang is sharing nuclear technology, US cables published by WikiLeaks on Friday showed.

A November 2009 cable from Larry Dinger, US Charge d'Affaires in Yangon, said cooperation between the two countries, regarded as pariahs by most of the international community, "remains opaque".

"Something is certainly happening," the cable said. "Whether that something includes 'nukes' is a very open question which remains a high priority for embassy reporting."

Myanmar's military government has long been suspected of trying to develop nuclear capability with help from Pyongyang, but most analysts believe the impoverished southeast Asian nation remains well short of its goal.

In September, Myanmar told the International Atomic Energy Agency that it had no aspirations to develop nuclear weapons and that its nuclear activities were purely for peaceful uses. It did not specify exactly what kind of nuclear work was taking place inside Myanmar.

A series of cables from the US embassy in Yangon, part of a new batch of documents released by Wikileaks, shows diplomats have been monitoring the mysterious activities of North Koreans in Myanmar for years, particularly at a site near the town of Mimbu persistently rumoured to be a planned nuclear facility.

For a graphic of the suspected nuclear site, click here

A cable in January 2004 said a foreign businessman had told the embassy of rumours that a nuclear reactor was being built near Mimbu, and that he had seen massive barges being unloaded near the site as well as a new airport in the area with a runway so large that "you could land the space shuttle on it".

The cable noted that rumours of a planned nuclear facility in the area had begun circulating in 2002, and there had been an increasing number of sightings of North Koreans in Myanmar.

An August 2004 cable said an informant had reported that North Korean workers were assembling surface-to-air missiles and constructing an underground facility at a Burmese military site near Mimbu. It said that while the report was not verified, it matched information gathered from other sources.

"This account is perhaps best considered alongside other information of various origins indicating the Burmese and North Koreans are up to something, something of a covert military or military-industrial nature," it said. "Exactly what, and on what scale, remains to be determined."