The leaders of North and South Korea are due to meet at a summit next month, Seoul’s envoy says.
It will be the first such meeting for more than a decade and the first since Kim Jong-un took power in North Korea.
The envoy also said Mr Kim suggested he would be willing to discuss getting rid of nuclear weapons, but only if his country’s security could be guaranteed.
In previous programmes to halt its nuclear ambitions, the North has failed to keep its promises.
Mr Kim and South Korean President Moon Jae-in will meet on the heavily fortified border next month, at the truce village of Panmunjom. The two countries also agreed to open a hotline between the leaders.
After returning from a rare trip to Pyongyang, South Korean officials said Mr Kim told them there would be no missile tests while diplomacy continued.
This is a huge turnaround for North Korea’s young leader, the BBC’s Laura Bicker reports from Seoul.
The United States had said talks with North Korea would only go ahead if it was willing to discuss denuclearisation.
The US has said it is “cautiously optimistic” about improving North-South contacts, but ruled out formal talks with Pyongyang unless it was ready to give up its nuclear weapons.
“The World is watching and waiting!” tweeted President Trump.
“May be false hope, but the U.S. is ready to go hard in either direction!”
Throughout the Olympics, North and South Korea struck a friendly tone, sending athletes to compete in a joint team and holding talks.
But the US maintained that North Korean gestures of rapprochement would carry little weight without a commitment on nuclear weapons – particularly following last year’s nuclear and missile tests carried out by the North.
Analysis by Jonathan Marcus, BBC defence correspondent
This is, of course, South Korea’s take on what North Korea is offering.
Some of the suggestions are, at face value, encouraging – not least North Korea’s apparent willingness to discuss the denuclearisation of the Korean peninsula. However, its conditions – that the military threat to North Korea is reduced and regime safety is guaranteed – raise all sorts of questions.
The North also says that it is willing to talk to the US with the goal of normalising relations with Washington.
The most positive element is the most immediate; that the period of calm initiated by the Winter Olympics looks set to continue.
“While the dialogues continue,” the South says, “the North will not conduct any nuclear tests, missile launches or other provocations.” (Surely not Pyongyang’s words!)
The two Koreas appear willing to create diplomatic space to try to improve relations across the board. Much will now depend upon how Washington reacts.
South Korean officials had dinner with the normally reclusive leader on Monday. Among the delegation were intelligence chief Suh Hoon and National Security Adviser Chung Eui-yong.
They were the first officials from Seoul to meet Mr Kim since he came to power. They returned to Seoul on Tuesday morning, the South Korean news agency Yonhap said.
The South Korean delegation is expected to visit Washington later this week to brief US officials on their talks in the North.
Kim Jong-un has met very few foreign officials since he became leader in 2011 and the last time envoys from the South visited Pyongyang was in 2007.
Two previous summits were held in 2000 and 2007, under South Korean presidents Kim Dae-jung and Roh Moo-hyun who met Kim’s father, Kim Jong-il.
So the sight of a southern delegation smiling, shaking hands and sitting down for dinner with him is significant.
They were aiming to capitalise on the reduced tensions after the Games, which saw the Koreas march together under a single flag.
The hope is that future formal talks will break the diplomatic standoff between the US and North Korea and persuade North Korea to abandon its nuclear weapons, something it has fiercely resisted despite ever-increasing punitive sanctions.
The North’s KCNA news agency said Mr Kim had “warmly welcomed” the delegates and held an “openhearted talk” with them.
They passed on a letter from South Korean President Moon Jae-in in which he invited Mr Kim to attend further talks.
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KCNA said Mr Kim had “exchanged views and made a satisfactory agreement” on the letter and gave orders for it to be acted on.
The dinner, which lasted four hours, also featured Ri Sol-ju, Mr Kim’s wife who rarely appears at official events, and his sister Kim Yo-jong, who was part of a North Korean delegation to the Pyeongchang Olympics.
The South’s response to the apparently cordial meeting is likely to remain muted until the delegates return to Seoul.
Officials have stressed the talks were only preliminary, but the parties had “somewhat shared” views on some issues.
When asked whether nuclear disarmament had been discussed, a senior officials from Mr Moon’s office said “I assume so”, the Yonhap news agency reports.