WASHINGTON - THE US Navy is monitoring a North Korean ship at sea under new UN sanctions that bar Pyongyang from exporting weapons, including missile parts and nuclear materials, US officials said on Thursday.

Officials said the vessel, called Kang Nam, is based in North Korea and became 'a subject of interest' after leaving a North Korean port on Wednesday. They could not confirm media reports describing the vessel as North Korean flagged.

The officials, who spoke on condition of anonymity, could not say what the ship, now in international waters, might be carrying.

One official said the Kang Nam would be the first North Korean ship to be monitored under the authority of the UN sanctions adopted last week after Pyongyang raised tensions by test-firing missiles, restarting a plant to produce arms-grade plutonium and conducting a May 25 nuclear test.

The Navy and the Pentagon both declined to comment on the vessel.

The UN Security Council approved a resolution last Friday that banned all weapons exports from North Korea and most arms imports into the country. It authorized UN member states to inspect North Korean sea, air and land cargo, requiring them to seize and destroy shipped goods that violate the sanctions.

Admiral Mike Mullen, chairman of the US Joint Chiefs of Staff, declined to discuss specifics when asked about the ship at a briefing on Thursday.

Adm Mullen, the highest-ranking officer in the US military, stressed the UN resolution would allow the Navy to search a ship only with permission. If a vessel refused to allow a search, Adm Mullen said the home country of any port where the vessel docks would be required to search its cargo.

Defence Secretary Robert Gates said the Obama administration was also concerned about the possibility of North Korea firing off more missiles, possibly in the direction of Hawaii.

Mr Gates said he had directed the redeployment of anti-missile assets in the Pacific region, including advanced radar and other defensive systems capable of bringing down medium-range ballistic missiles as a precaution. -- REUTERS