The United States sees no sign of a major nuclear weapons programme in Myanmar and hopes that the new regime will boost cooperation with the UN atomic watchdog, a US official said.

"We've looked at this fairly carefully and we do not see signs of a substantial effort at this time" on nuclear arms, the official told reporters accompanying Secretary of State Hillary Clinton on a landmark visit.

While Clinton will raise concerns about links to North Korea, the State Department official downplayed accounts by defectors that Myanmar has worked with Pyongyang to develop an advanced nuclear weapons system.

He said that the "primary" US concern was missile technology. In May, a US Navy destroyer intercepted a North Korean cargo ship in the South China Sea suspected of carrying missile parts to Myanmar.

Myanmar has "talked to us seriously about potential steps associated with the IAEA and other actions they are contemplating with respect to North Korea," the official added, referring to the UN's International Atomic Energy Agency.

The official, who spoke on condition of anonymity, said this could include signing an additional protocol granting the IAEA greater inspection authority.

The United States will seek assurances of "a determination on the part of the government to discontinue activities that we believe are antithetical to the maintenance of peace and stability," he said.

In late 2010 the UN atomic watchdog asked Myanmar to be allowed to visit a number of suspect nuclear sites and facilities.

Clinton arrived in Myanmar Wednesday to test the waters of nascent reforms in the long-isolated nation, which this year nominally ended decades of military rule and launched dialogue with the opposition and ethnic minorities.

Senator Richard Lugar, the top member of the rival Republican Party on the Senate Foreign Relations Committee, has urged Clinton to put a top priority on assessing ties between North Korea and Myanmar.

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