Military-ruled Myanmar has begun a nuclear weapons programme with the help of North Korea, according to an investigation Friday, citing a senior army defector and years of "top secret material".

A new documentary shows thousands of photos and defector testimony revealing the junta's nuclear ambitions and a secret network of underground tunnels, allegedly built with help from North Korea, television network Al Jazeera said.

The revelations prompted a US senator to abruptly cancel a trip to Myanmar, formerly known as Burma, and the United States raised fresh concerns about "growing military ties" between the two pariah states.

Norway-based news group Democratic Voice of Burma (DVB), which produced the film, says "evidence of Myanmar's nuclear programme has come from top-secret material smuggled out of the country over several years," Al Jazeera reported.

The years-long investigation included hundreds of files and other evidence from a Myanmar defector, army major Sai Thein Win, who said he was deputy commander of a military factory heading up Myanmar's nuclear battalion.

"They really want to build a bomb. That is their main objective," he is quoted as saying in the film, broadcast by Al Jazeera on Friday.

A senior Myanmar official, asking not to be named, told AFP that the accusations were "groundless", without elaborating.

But the United States said it was worried about the military links between the two nations, said Geoff Morrell, a spokesman for Defence Secretary Robert Gates who is in the region for an Asian security summit.

"We are concerned with growing military ties with the DPRK (North Korea) and are following it closely to ensure that the multiple UNSCRs (UN Security Council resolutions) are enforced," Morrell told AFP in an email.

Morrell did not comment directly on the nuclear allegations.

US Senator Jim Webb was due to fly to Myanmar on Thursday but said it would be "unwise and potentially counter-productive" until there is further clarification on the suspicions of cooperation with nuclear-armed North Korea.

The findings "contain new allegations regarding the possibility that the Burmese government has been working in conjunction with North Korea in order to develop a nuclear programme," Webb said.

Files reportedly smuggled out of Myanmar by Sai Thein Win have been seen by experts including Robert Kelley, former director of the International Atomic Energy Agency.

"It appears it is a nuclear weapons programme because there is no conceivable use for this for nuclear power or anything like that," he is quoted as saying on Al Jazeera's website.

Myanmar, which has been military ruled since 1962, has previously been accused of violating a UN Security Council ban on North Korean arms exports, which was imposed last June.

Following a visit there in May, US Assistant Secretary of State for East Asian and Pacific Affairs Kurt Campbell expressed concern about a suspected arms shipment from North Korea to Myanmar.

He called for a "transparent process" to be put in place as a way for Myanmar to assure the international community of its commitments to the resolution on North Korean arms.

President Barack Obama's administration last year launched a dialogue with Myanmar's military rulers, after concluding that Western attempts to isolate the regime had met with little success.

But Washington has sharply criticised preparations for this year's elections -- the first in 20 years -- as well as raising the nuclear concerns.