Guterres said recent moves by South and North Korea to ease tensions were important, but he added: "let's not forget that the essential problem is yet to be solved."
"I believe war is avoidable," Guterres told reporters, but he added: "I am not yet sure that peace is guaranteed."
The UN chief said his goal was to ensure that "those who are more relevant in this process are able to seriously talk to each other and seriously find a way to denuclearization."
The United States and North Korea have shown little interest in holding direct talks to address the crisis.
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Presenting his priorities for 2018 to the General Assembly, Guterres said there were "small signs of hope" after North Korea agreed to take part in the Winter Olympics in the South and the re-opening of a military hotline between Pyongyang and Seoul.
Guterres will attend the opening ceremony of the Pyeongchang Games next month.
North Korea's race to build an intercontinental ballistic missile capable of hitting the United States with a nuclear warhead has raised fears of a devastating conflict.
Trump's administration has been adamant that North Korea must first freeze its military programs before talks can take place.
The United States has led the drive at the Security Council to ratchet up economic sanctions on North Korea such as restrictions on oil supplies that were adopted in December.