The Obama administration says it is prepared to confront ships believed to be carrying contraband materials to North Korea but will not try to forcibly board them.
U.S. ambassador to the United Nations Susan Rice said Friday that U.S. officials would seek permission to board and inspect such vessels in a bid to curb North Korea's nuclear weapons ambitions.
She said the ships would be directed to a nearby port for inspection if they could not be boarded at sea.
The U.N. Security Council on Friday punished North Korea for its second nuclear test by imposing tough new sanctions.
Rice said it would not be surprising if North Korea reacted to the sanctions with "further provocation."
Rice said: "There's reason to believe they may respond in an irresponsible fashion to this."
But she said the U.S. will focus on the enforcement of the multilateral sanctions, which she said she expects to have significant impact on North Korea's financing of its weapons and missile.