North Korea faces more US sanctions
The Obama administration has tried to pile more pressure on North Korea by announcing expanded and strengthened sanctions against the communist-led government and its nuclear weapons programme.
The fresh round of sanctions was announced by US secretary of state Hillary Clinton during a visit to Seoul, South Korea, but officials in Washington said the moves would not be ready to be put in place for another two weeks.
But in the past, similar tactics have been undercut by North Korea's knack for finding loopholes and escape hatches.
Mrs Clinton left South Korea for a trip to the Vietnamese capital Hanoi for events marking the 15th anniversary of normalised US-Vietnam relations.
Mrs Clinton arrived for two days of talks that will include a regional security forum with senior officials from around South-East Asia. Those discussions are expected to focus largely on the threat posed by North Korea.