South Korean officials who met with North Korea's Kim Jong-un this week head to Washington on Thursday, seeking to reassure the US ahead of negotiations about ending Pyongyang's nuclear weapons program and preventing the outbreak of war.
In the first meeting of its kind, the South Korean officials said Mr Kim expressed his willingness to denuclearise the Korean peninsula if his country's security is assured.
- US President Donald Trump sees 'progress' on North Korea talks
- Auckland would face 250k casualties in North Korean attack
- North Korea's hit-list: The cities it wants to destroy
US President Donald Trump said North Korea seems "sincere" in its apparent willingness to halt nuclear tests if it held denuclearisation talks with the United States.
However South Korean president Moon Jae-in downplayed optimism over Pyongyang's offer.
"I believe it is still too early to be optimistic because we are only at the starting line," Mr Moon said, according to Yonhap news agency.
Mr Moon also added he has no plans yet of urging an easing of international sanctions against the North Korea.
Next month, North Korea and South Korea will have the first meeting between their leaders since 2007 at the border village of Panmunjom, said Chung Eui-yong, head of the South Korean delegation.
Leaders around the world have met the apparent breakthrough with guarded optimism, wary of repeating past negotiations that failed to prevent Pyongyang from developing nuclear weapons and intercontinental ballistic missiles (ICBMs).
Japan's Chief Cabinet Secretary Yoshihide Suga said on Wednesday it was "extremely important" that North Korea show its commitment and concrete actions toward abandonment of its nuclear missile development in a complete, verifiable and irreversible way.
Mr Chung, South Korea's National Security Office head, has close contacts in the US, and National Intelligence Service chief Suh Hoon, who is known as South Korea's top North Korea negotiator, will be making the trip to Washington on Thursday.
Mr Chung said he had a message from Mr Kim he will relay to US officials, but it was not clear whether he would meet with Mr Trump.
After returning from the US, the South Korean officials will split up and Mr Chung will visit China and Russia, while Mr Suh will head to Japan to speak to officials in the respective countries on the latest detente with North Korea.
Mr Trump told reporters the US had "come a long way, at least rhetorically" with North Korea and "statements coming out of South Korea and North Korea have been very positive".
Asked if he had any preconditions for talks, Mr Trump said, "I don't want to talk about it. We're going to see what happens."
Chinese state-run tabloid the Global Times published an editorial warning the Korean nuclear issue cannot be solved without China, Russia and the United Nations Security Council.
"The reality is that North Korea now has an intercontinental ballistic missile that can allegedly hit targets in the US," the paper wrote. "No one can intimidate anyone. Negotiation is the only way out."