The United States must press Myanmar to reveal the state of its nuclear program and any ties with North Korea as a condition for better relations, a key US lawmaker urged Monday.

"An early goal of the tentative US re-engagement with Burma should be full disclosure of the extent and intent of the developing Burmese nuclear program," said top Senate Foreign Relations Committee Republican Richard Lugar.

Lugar's comment came as US Secretary of State Hillary Clinton prepared to become the most senior US official in 50 years to visit Myanmar, also known in Washington as Burma, to test the waters after dramatic -- but tentative -- reforms by its military-backed government.

"The United States is appropriately testing the appearance of reforms within Burma," said Lugar, one of his party's most respected voices on world affairs.

But "missing from the long list of good intentions has been reference to the growing relationship between North Korea and Burma, and close cooperation between their two militaries," he said in a statement.

Lugar said the Senate Foreign Relations Committee had sounded the alarm five years ago over Myanmar's reported intention to get North Korea's help to develop nuclear weapons.

"The sincerity with which a wide range of reforms has been promised by the Burmese government must be judged by whether the words are followed by actions," he said.

Myanmar media in June quoted a top government official as saying that the country was too poor to get nuclear weapons and had halted its nuclear research program.

US diplomatic memos released last year by the website WikiLeaks said Washington has suspected for years that Myanmar ran a secret nuclear program supported by Pyongyang.

A UN report released in November 2010 said North Korea was supplying banned nuclear and ballistic equipment to Myanmar, along with Iran and Syria.