Update 6pm: North Korean leader Kim Jong Un has expressed a willingness to discuss nuclear disarmament with the US and impose a moratorium on nuclear and missile tests during such talks, a senior South Korean official has said.
Mr Kim also agreed to meet South Korea's president at a tense border village in late April, presidential national security director Chung Eui-yong said after talks with Mr Kim in Pyongyang, North Korea's capital.
The North's reported willingness to hold a "candid dialogue" with the US to discuss denuclearisation and establish diplomatic relations follows a year of increased fears of war on the Korean peninsula, with Mr Kim and US President Donald Trump exchanging fiery rhetoric and crude insults over Mr Kim's barrage of weapons tests.
The Trump administration also pushed through some of the harshest sanctions the already hugely sanctioned North has yet faced.
Mr Trump tweeted that "possible progress" was being made in the talks with North Korea, and that all sides were making serious efforts.
He added: "May be false hope, but the US is ready to go hard in either direction!"
Possible progress being made in talks with North Korea. For the first time in many years, a serious effort is being made by all parties concerned. The World is watching and waiting! May be false hope, but the U.S. is ready to go hard in either direction!— Donald J. Trump (@realDonaldTrump) March 6, 2018
There is still scepticism whether the developments will help establish genuine peace between the Koreas, which have a long history of failing to follow through with major agreements.
The US has made it clear it does not want empty talks with North Korea and that all options, including military measures, remain on the table.
The North has repeatedly said in the past that it will not negotiate over its nuclear programme and vowed to bolster its nuclear and missile arsenals.
Its apparent about-face might be an attempt to win concessions as its economy struggles under the weight of sanctions, some analysts said, or a way to buy time to better develop nuclear missiles targeting the mainland US.
Many experts believe North Korea will not easily give up a nuclear programme it has doggedly developed, despite years of escalating international pressure, to cope with what it claims is US hostility.
Mr Chung led a 10-member South Korean delegation on a two-day visit to North Korea. They were the first South Korean officials to meet the young North Korean leader since he took power after his dictator father's death in late 2011.
The trip also was the first known high-level visit by South Korean officials to the North in about 11 years.
It followed a series of co-operative steps taken by the Koreas during last month's Pyeongchang Winter Olympics hosted by South Korea.
If talks with the US happen, Mr Chung said North Korea "made it clear that it won't resume strategic provocations like additional nuclear tests or test-launches of ballistic missiles" while the talks continue.
Pyongyang told the South Korean envoys it would not need to keep its nuclear weapons if military threats against it are removed and it receives a credible security guarantee, Mr Chung said.
He said the North promised not to use its nuclear and conventional weapons against South Korea.
Mr Kim also said he "understands" that contentious annual military drills by the US and South Korea will take place in April at a scale similar to previous years and expressed hope they could be modified once the situation on the Korean peninsula stabilises, according to a senior South Korean presidential official.
Mr Chung said the two Koreas agreed to hold their summit at a Seoul-controlled facility inside the border village. He also said Mr Kim and liberal South Korean President Moon Jae-in will establish a "hotline" communication channel between them to lower military tensions, and would speak together before the planned summit.
Earlier: North and South Korea agree to hold talks
North Korean leader Kim Jong Un has agreed to hold a landmark summit with South Korea's president and impose a moratorium on nuclear and missile tests if his country holds talks with the US, a senior Seoul official said.
Chung Eui-yong, South Korea's presidential national security director, said the two Koreas agreed to hold their third-ever summit at a tense border village in late April.
He also said the leaders will establish a "hotline" communication channel to lower military tensions, and would speak together before the planned summit.
Mr Chung led a 10-member South Korean delegation that met Mr Kim during a two-day visit to Pyongyang, North Korea's capital. They returned on Tuesday.
The agreements follow a flurry of co-operative steps taken by the Koreas during last month's Pyeongchang Olympics in South Korea.
Tensions had run high during the previous year because of a barrage of North Korean weapons tests.
The two past summits, in 2000 and 2007, were held between Mr Kim's late father, Kim Jong Il, and two liberal South Korean presidents.
They resulted in a series of co-operative projects between the Koreas that were scuttled during subsequent conservative administrations in South Korea.
Mr Chung said North Korea had agreed to suspend nuclear and missile tests for as long as it holds talks with the US.
Pyongyang also made it clear it would not need to keep its nuclear weapons if military threats against it are removed and it receives a credible security guarantee, Mr Chung said.
Earlier: North Korea's Kim Jong Un had 'openhearted talk' with Seoul envoys
North Korean leader Kim Jong Un had an "openhearted talk" in Pyongyang with envoys for South Korean President Moon Jae-in, the North said on Tuesday.
It is the first time South Korean officials have met with the young North Korean leader in person since he took power after his dictator father's death in late 2011 - and the latest sign that the Koreas are trying to mend ties after a year of repeated North Korean weapons tests and threats of nuclear war.
North Korea's state media said Mr Kim expressed his desire to "write a new history of national reunification" during a dinner on Monday night that Seoul said lasted about four hours.
Given the robust history of bloodshed, threats and animosity on the Korean Peninsula, there is considerable scepticism over whether the Koreas' apparent warming relations will lead to lasting peace.
North Korea, some believe, is trying to use improved ties with the South to weaken US-led international sanctions and pressure, and to provide domestic propaganda fodder for Mr Kim.
But each new development also raises the possibility that the rivals can use the momentum from the good feelings created during North Korea's participation in the South's Pyeongchang Winter Olympics last month to ease a standoff over North Korea's nuclear ambitions and restart talks between Pyongyang and Washington.
The North Korean report sought to make Mr Kim look statesmanlike as he welcomed the visiting South Koreans, with Mr Kim offering views on "activating the versatile dialogue, contact, cooperation and exchange".
He was also said to have given "important instruction to the relevant field to rapidly take practical steps for" a summit with Mr Moon, which the North proposed last month.
Mr Moon, a liberal who is keen to engage the North, likely wants to visit Pyongyang. But he must first broker better ties between the North and Washington, which is Seoul's top ally and its military protector.
The role of a confident leader welcoming visiting, and lower-ranking, officials from the rival South is one Mr Kim clearly relishes. Smiling for cameras, he posed with the South Koreans and presided over what was described as a "co-patriotic and sincere atmosphere".
Many in Seoul and Washington will want to know if, the rhetoric and smiling images notwithstanding, there is any possibility Mr Kim will negotiate over the North's breakneck pursuit of an arsenal of nuclear missiles that can viably target the US mainland.
The North has repeatedly and bluntly declared it will not give up its nuclear bombs. It also hates the annual US-South Korean military exercises that were postponed because of the Olympics but will likely happen later this spring. And achieving its nuclear aims rests on the North resuming tests of missiles and bombs that set the region on edge.
Photos distributed by the North showed a beaming Mr Kim dressed in a dark Mao-style suit and holding hands with Mr Moon's national security director, Chung Eui-yong, the leader of the 10-member South Korean delegation. Mr Chung's trip is the first known high-level visit by South Korean officials to the North in about a decade.
The South Korean delegates have another meeting with North Korean officials on Tuesday before returning home, but it is unclear if Mr Kim will be there.
He was said to have expressed at the dinner his "firm will to vigorously advance the north-south relations and write a new history of national reunification by the concerted efforts of our nation to be proud of in the world".