Myanmar risks destabilizing Southeast Asia through its pursuit of weapons, although it is not yet clear whether the military regime is developing a nuclear program, a US official said Thursday.

A senior army defector, in a recent documentary broadcast on Al Jazeera television, said the junta has been seeking nuclear weapons and developing a secret network of underground tunnels with help from North Korea.

Scot Marciel, the State Department official in charge of Southeast Asia, said that the United States was still assessing the allegations about Myanmar -- also known as Burma.

"I think there's two issues. One is whether there is some kind of serious nuclear program in Burma, which certainly would be tremendously destabilizing to the entire region," Marciel testified at a congressional hearing.

"There's also the Burmese acquisition of other military equipment -- conventional -- which also can affect regional stability," he said.

"We're looking at both of those questions very closely," said Marciel, the deputy assistant secretary of state for East Asian affairs.

A senior Myanmar official last week told AFP that the accusations of a nuclear program were "groundless," without elaborating.

On a visit to Myanmar in May, Marciel's superior, Assistant Secretary of State Kurt Campbell, expressed concern about a suspected arms shipment from North Korea and sought assurances from the regime.

Senator Jim Webb, one of the most vocal US advocates of engagement with Myanmar, abruptly canceled a visit to the country earlier this month due to the allegations of cooperation with North Korea.

Addressing the Asia Society on Wednesday, Webb said he was still waiting to learn more about the allegations but decided it would be counterproductive to visit Myanmar at the time the documentary was broadcast.

President Barack Obama's administration last year opened dialogue with Myanmar, concluding that the previous approach of isolating the regime had not borne fruit.

But the administration has voiced deep concern about elections later this year, which the opposition considers a sham to legitimize military rule.