North Korea has sought security guarantees from the U.S. and relief from worldwide sanctions.
South Korea's president said Tuesday no timeframe has been set for a historic visit to Seoul by North Korean leader Kim Jong Un despite both hoping it will take place this year.
"This will be the first time that a North Korean leader will visit South Korea so, although there is no time frame set for that, still that's very meaningful", he continued, adding that a Seoul summit would help improve relations between the USA and North Korea.
"The message is that President Trump has very favourable views towards Chairman Kim and he likes him", Mr Moon told reporters aboard a flight from Argentina to New Zealand, where he started a three-day state visit on Sunday.
Ardern met with Moon on the sidelines of the East Asia Summit and Apec last month, and he has visited New Zealand in 2006 and in 2015.
Donald Trump wants North Korean leader Kim Jong Un to know that he likes him and will fulfil his wishes, South Korea's president Moon Jae-in said on Sunday, a day after meeting the United States president at an economic summit in Argentina.
"We're getting along very well", Trump said aboard Air Force One on Thursday as he prepared to travel to the G20 summit in Buenos Aires, Argentina.
After sharply raising tensions with nuclear and missile tests past year, Kim abruptly reached out to Moon and Trump with a vague nuclear disarmament pledge.
In his talks with Trump in Argentina, Moon earned some support for the Seoul summit from the USA leader - perhaps in a bid to entice Kim to make good on his pledge.
If Kim, a third-generation hereditary ruler, visits Seoul, he would be the first North Korean leader to do so since the end of the 1950 to 1953 Korean War.
He said such a visit would "accelerate the denuclearisation in the Korean peninsula" and result in a "greater stride in relations improvement" between the North and the United States. In June, Trump and Kim opened up dialogue on denuclearisation of the Korean peninsula after months of trading military threats and pointed barbs.