U.S. law requires a cut-off in U.S. nuclear cooperation and in financial assistance to any state Washington believes should be non-nuclear that detonates a nuclear weapon. North Korea falls into that category.

The sanctions imposed by the president require the cut-off in nuclear cooperation and in financial assistance. But since the United States does not provide either to North Korea, the sanctions put in place by Bush have little practical impact.

U.S. humanitarian assistance is not affected and will continue, a White House official said.

"These sanctions in no way undermine the president's long-standing commitment to providing humanitarian assistance to alleviate the suffering of the North Korean people and the commitment to denuclearize North Korea through the six-Party talks," the official said.

The order by Bush did not affect a separate effort by the U.S. government to make it harder for North Korean leader Kim Jong-il to acquire luxury items such as cognac, jet skis and plasma televisions.

The United States, South Korea, Japan, Russia and China -- the other five nations in stalled six-party talks -- have dangled promises of assistance if North Korea agrees to give up nuclear weapons.

They said they would provide the North with energy assistance and to consider, at an appropriate time, providing Pyongyang with light-water nuclear reactors; normalizing relations, and negotiating a peace treaty.

No date for another round of the six-party negotiations has been announced. Russian officials predicted it would not take place until 2007 but a U.S. official said Washington had not given up on negotiations in December.