Four U.S. nuclear experts left North Korea Friday, after Pyongyang ordered the expulsion of inspectors monitoring nuclear disarmament measures.
United Nations inspectors departed the country Thursday after removing seals and disabling surveillance cameras at the Yongbyon atomic facility.
The North Korean government expelled the inspectors after the United Nations adopted a statement condemning Pyongyang for its April 5 rocket launch. North Korea also withdrew from six-nation disarmament talks, and vowed to restart production of its weapons-grade plutonium.
The United States has warned that North Korea will face consequences for expelling the inspectors. Washington proposed additions to a U.N. sanctions list Wednesday.
The U.N. Security Council sanctions committee is to report by April 24 on North Korean companies or technology that should be added to the current list.
Countries involved in the denuclearization talks have called on Pyongyang to return to the negotiating table.
Meanwhile, South Korea is preparing to announce plans to fully join the Proliferation Security Initiative (PSI). The U.S.-led initiative is aimed at preventing the global trafficking of weapons of mass destruction. More than 90 member countries track and stop vessels suspected of carrying such weapons.
North Korea has warned it would interpret Seoul's decision to join the PSI as a declaration of war. But a spokesman for South Korea's Foreign Ministry said it will be impossible to stop North Korean ships in international waters because the North is not part of the initiative.