North Korean leader Kim Jong-un has given his first time line for denuclearisation, aiming for the end of US President Donald Trump's first term, Seoul officials said on Thursday, prompting thanks from Mr Trump who said they would "get it done together".
Mr Kim and South Korean President Moon Jae-in will also meet in Pyongyang on September 18 to 20 and will discuss "practical measures" toward denuclearisation, President Moon's national security adviser, Chung Eui-yong, said on Thursday after meeting Mr Kim a day earlier.
The summit could in turn provide renewed momentum to talks over denuclearlisation between North Korea and the United States, after President Trump cancelled a visit to the North by his secretary of state last month citing a lack of progress.
North Korea's told South Korean officials his faith in President Trump was "unchanged" and he wanted denuclearisation and an end to hostile relations with the United States within President Trump's first term in office, ending in early 2021, Mr Chung said.
"He particularly emphasised that he has never said anything negative about President Trump," Mr Chung said.
Mr Trump welcomed Mr Kim's remarks in a trademark tweet.
"Kim Jong Un of North Korea proclaims 'unwavering faith in President Trump.' Thank you to Chairman Kim. We will get it done together!" he wrote.
North Korea has said in previous, failed talks over the years that it could consider giving up its nuclear programme if the US provided security guarantees by removing its troops from South Korea and withdrawing its so-called nuclear umbrella of deterrence from South Korea and Japan.
US officials involved in negotiations have said North Korea has refused to even start discussions about defining "denuclearisation" or other key terms such as "verifiable" and "irreversible", and have insisted the US must first agree to take simultaneous steps to reduce economic pressure.
Mr Chung said President Kim had stressed the need for the US to reciprocate North Korea's initial moves, which have included dismantling a nuclear test site and a missile engine facility.
The US Embassy in Seoul on Thursday said it had no information to share on the matter.
North Korea's official KCNA news agency said Mr Kim told Mr Chung and other envoys that it was his "fixed stand" to turn the Korean peninsula into "the cradle of peace without nuclear weapons and free from nuclear threat".
Mr Chung said Mr Kim showed "frustration over the doubt raised by some parts of the international community about his willingness to denuclearise, and asked us to convey his message to the United States".
"He said he would appreciate that such good faith is accepted with good faith," Mr Chung said. "He expressed his strong will to carry out more proactive measures toward denuclearisation if action is taken in response to the North's preemptive steps."
The two Koreas also plan to open an inter-Korean liaison office before the third summit in the North's border city of Kaesong, staffed by officials from both sides to facilitate consultation, Mr Chung said.
Mr Kim and Mr Trump held a landmark summit in Singapore in June, in which they agreed to work toward complete denuclearisation. But negotiations have made little headway, while signs North Korea has maintained work on its weapons have emerged.
In this year's talks, North Korea and the US have been at odds over whether denuclearisation or declaring an end to the 1950-53 Korean War should come first.
The war ended with an armistice, not a peace treaty, meaning US-led UN forces, including South Korea, are technically still at war with the North.
North Korea has long sought a formal end to the war but US officials have said an end-of-war declaration could weaken North Korea's incentive for denuclearisation, and raise questions about the 28,500 US troops stationed in South Korea, a legacy of the three-year war.
US officials also say they have already made concessions, such as halting joint military exercises with South Korea.
US Secretary of State Mike Pompeo visited Pyongyang in July, after which North Korea accused him of making "unilateral and gangster-like demands for denuclearisation" while showing little interest in ending the war.
The US, however, has said it is committed to building a peace mechanism if North Korea denuclearises.
"Looks like Kim is trying to wash away worries that talks could stall or fail, knowing well that Washington is losing patience," said Koh Yu-hwan, a professor of North Korean Studies at Dongguk University in Seoul.
"Kim also made it clear that he needs some kind of proof Trump has abandoned the US's hostile policy before moving toward denuclearisation. Kim is trying to prove his sincerity."