Guterres made the comments to reporters after meeting with Japanese Prime Minister Shinzo Abe in Tokyo just days after US Secretary of State Rex Tillerson offered to begin direct talks with North Korea without pre-conditions.
The White House said on Wednesday that no negotiations could be held with North Korea until it improves its behaviour. The White House has declined to say whether President Donald Trump, who has taken a tougher rhetorical line toward Pyongyang than Tillerson, gave approval for the top US diplomat's overture.
Japan has insisted that now is the time to keep up maximum pressure on Pyongyang, not start talks on the North's missile and nuclear programmes. United Nations political affairs chief Jeffrey Feltman, who visited Pyongyang last week, said on Tuesday senior North Korean officials did not offer any type of commitment to talks, but he believes he left "the door ajar".