Former UN Secretary-General Ban Ki-moon has urged South Korea to cooperate more with the international community to maintain sanctions on North Korea.
Ban, who headed the United Nations for 10 years until 2016, gave a speech in Seoul on Tuesday.
He referred to last month's second summit between US President Donald Trump and North Korean leader Kim Jong Un, which failed to reach agreement.
Ban said Pyongyang tried to reach a compromise with Washington by freezing its nuclear weapons, instead of abandoning them.
He said Trump clearly rejected North Korea's tactics to make a step-by-step deal, and that such negotiating maneuvers will lead in a favorable direction.
Ban also said that North Korea, which is apparently confused after the summit breakdown, might take a harsher stance.
He stressed the importance of the US-South Korea alliance and urged President Moon Jae-in's administration not to unilaterally push forward with inter-Korean projects. He said that for the time being, full-fledged economic cooperation with the North will be impossible.