Burma may be building missile and nuclear sites in remote locations with support from North Korea, according to secret US cables released by Wikileaks.
The documents cite witnesses who say North Korean workers are helping Burma construct an underground bunker in a remote jungle.
The move underlines concern that the Burmese regime might be trying to build a nuclear weapon, despite denials.
Wikileaks has so far released more than 1,100 of 251,000 diplomatic cables.
The reports, which stretch over the past six years, suggest dockworkers and foreign businessmen have seen evidence of alleged sites.
A cable dating from August 2004 spoke of a Burmese officer in an engineering unit who said surface-to-air missiles were being built at a site in a town called Minbu in west-central Myanmar.
"The North Koreans, aided by Burmese workers, are constructing a concrete-reinforced underground facility that is '500ft from the top of the cave to the top of the hill above'," reads the cable, published by the Guardian newspaper.
Some 300 North Koreans were working at the site, the authors said, although the cable suggested this number was improbably high.
'Jigsaw of information'
An expatriate businessman also told the US Embassy in Rangoon that he had heard rumours of a nuclear site being built.
According to another cable, the businessman told an embassy officer about rumours of a large barge unloading reinforced steel which looked as if it was for a project larger than a factory.
Analysts have previously raised concerns that Burma is co-operating with North Korea to develop nuclear technology, although Burma has denied the claim.
The BBC's diplomatic correspondent Jonathan Marcus says that for months there have been persistent reports in the press and specialised journals suggesting that Burma is building a nuclear facility with North Korean help.
Those reports are mainly derived from clues pieced together from defectors and satellite imagery, he adds.
There is nothing in the cables to confirm what Burma and North Korea may be up to, but they do provide a fascinating insight into the jigsaw of information on which Western intelligence is based, our correspondent says.
Another cable released by the whistle-blowing site suggests that China, Burma's most powerful ally, is growing impatient with the country's leaders.
Two years ago, Chinese Ambassador Guan Mu told US diplomats that there was a risk of turmoil in Burma.
He suggested that the country's ruling generals would cede power if they were offered assurances that they would not "lose their lives" and if they could keep their economic interests.