WASHINGTON (AFP) - New UN sanctions intended to force North Korea to abandon its nuclear program will have an "impact" when they take full force, the top US envoy to the United Nations has said.

Susan Rice also said the United States was closely monitoring a North Korean ship that Washington suspects of transporting weapons and nuclear know-how in what would be a violation of a UN embargo on Pyongyang's arms sales.

"We're pursuing and following the progress of that ship very closely," Rice told CBS television's "Face the Nation," declining to provide details on any action the United States might take toward the Kang Nam 1 on the high seas.

A US Navy destroyer has been tracking the ship, which is suspected of being headed for Myanmar, for nearly two weeks.

The UN Security Council adopted resolution 1874 in response to North Korea's May 25 nuclear test. The resolution establishes a strengthened inspection regime for all cargo coming from or destined for North Korea, whether it is being transported by air, sea or ground.

Rice stressed that the new interdiction authorities granted by the resolution are "but one piece of a very tough, very comprehensive sanctions regime that we are going to pursue fully and implement and enforce fully and effectively."

The new UN sanctions also include a widening of the existing arms embargo on North Korea.

"When this resolution is fully enforced -- not only in terms of potential vessels that may be violating the sanctions but the financial sanctions, the arms embargo, the assets freezes -- this will be a very, very tough package that will have an impact on North Korea," Rice said.

South Korean President Lee Myung-Bak said meanwhile that his country and Japan "will never tolerate" a nuclear-armed North Korea after talks in Tokyo with Prime Minister Taro Aso.