North Korean leader Kim Jong-un has invited US President Donald Trump to formally meet.
South Korea's National Security Adviser Chung Eui-yong told reporters Mr Kim also said he was committed to denuclearisation, adding: "Kim pledged that North Korea would refrain any further nuclear missile tests."
"He expressed his eagerness to meet with Donald Trump as soon as possible," Mr Chung told reporters at the White House.
"President Trump appreciated the briefing and said he would meet Kim Jong-un by May to achieve permanent denuclearisation.
Mr Chung reaffirmed South Korea, the United States and its partners were committed to denuclearisation and a peaceful resolution.
White House national security adviser H.R. McMaster and other senior aides were briefed on Thursday (local time) by South Korean officials on their talks with North Korea this week.
US network CNN is reporting South Korean officials hand-delivered a letter from North Korean leader Kim Jong-un to the White House, citing a diplomatic source, according to Reuters.
Mr Chung is visiting Washington to brief US allies about his recent landmark talks with North Korean leader Kim Jong-un in Pyongyang.
South Korea announced on Tuesday the North had stated there was "no reason" to hold on to its nuclear weapons "if military threats towards the North are cleared and the security of its regime is guaranteed".
The North is open to "frank" talks with the United States on denuclearisation and would suspend missile and nuclear tests while dialogue was underway, Mr Chung said after returning from a meeting in Pyongyang with Kim.
Mr Trump welcomed the offer as "very positive".
However his Director of National Intelligence, Dan Coats, told Congress he was "quite skeptical" and Vice President Mike Pence said the US position towards North Korea would not change "until we see credible, verifiable, and concrete steps toward denuclearisation".
- with Reuters, additional reporting from Louise Cheer
