On a visit to North Korea's primary ally China, Clinton reiterated her view that Pyongyang's recent rocket launch showed that Kim Jong-Un's regime saw better relations with the world "not as a goal, but as a threat".

"The new leadership in Pyongyang still has the opportunity to change course and put their people first," Clinton told a session of the annual Strategic and Economic Dialogue between the two countries.

"If they focus on honouring their commitments and rejoining the international community, and on feeding and educating their citizens, the United States will welcome them and work with them," Clinton said, according to prepared remarks.

After long hesitation, the United States on February 29 reached an agreement with North Korea under which the regime would freeze its nuclear and missile programmes and Washington would provide badly needed food assistance.

Just weeks later, North Korea defiantly carried out what US officials considered a failed missile test, leading Washington to suspend the aid plan.

North Korea has since stepped up threats against US-allied South Korea and hinted that it may conduct its third nuclear test.

"Given North Korea's track record and recent actions, any reasonable observer must question their seriousness about improving relations or keeping their word," Clinton said.

Clinton gave a positive assessment on China's efforts, despite criticism from some US lawmakers who say that the rising Asian power should do more to rein in its ally.