Seoul, South Korea (CNN) North Korea is willing to talk to the United States about giving up its nuclear weapons, South Korea said Tuesday, in a remarkable development that followed unprecedented meetings in Pyongyang.

North Korean leader Kim Jong Un has also agreed to refrain from conducting nuclear and missile tests while engaging in dialogue with South Korea, Seoul's national security chief Chung Eui-yong said after returning from talks with Kim.

Chung said Pyongyang expressed willingness to talk to the United States "in an open-ended dialogue to discuss the issue of denuclearization and to normalize relations with North Korea."

It's a startling statement from a nation that only months ago declared it could wipe the United States off the face of the Earth.

"This is Kim Jong Un stepping on the peace offensive gas pedal," Duyeon Kim, a senior research fellow at the Korean Peninsula Future Forum in Seoul, said.

Key developments:

South Korean President Moon Jae-in and Kim will meet for a summit at the demilitarized zone that divides the two Koreas in April, Chung said

The two sides will open a hotline so the leaders could communicate directly with each other, according to Chung.

US President Donald Trump weighed in on the developments on Twitter, saying "the world is watching and waiting!"

The Trump administration has often said it's willing to negotiate with North Korea if it puts denuclearization on the table.

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

"The fixed policy of the United States of America is that we are going to continue with all options on the table to bring intensifying economic and diplomatic pressure to bear until North Korea, once and for all, completely and verifiably abandons its nuclear weapons and ballistic missile program," US Vice President Mike Pence said last month after visiting South Korea.

A win for Moon

The announcement represents a significant diplomatic accomplishment for South Korean President Moon Jae-in, who used the Winter Olympic Games to engineer a thaw in relations with the North that had previously seemed a distant prospect.

As part of the dialogue, the two Korean leaders would hold a summit next month, the first of its kind in more than a decade, Chung said.

The last inter-Korean summit was in 2007, when South Korean President Roh Moo-hyun met Kim's father, late North Korean leader Kim Jong Il.

The April summit will be held at the Panmunjom Peace House on the South Korean side of the demilitarized zone that divides the two countries, Chung said.

Moon sent Chung and four other top government officials to Pyongyang Monday , when they met with Kim and some of his top aides.

It's believed to be the first time the young North Korean leader has ever met with any officials from South Korea since taking power in 2011.

'Something to work with'

Though surprising, the statements from North Korea aren't a complete u-turn. Pyongyang has long maintained its development of nuclear weapons is a response to what it calls the US "hostile policy" toward the Democratic People's Republic of Korea, as the country is officially known.

"To some extent, this is a reiteration of something the North Koreans have said, that Kim Jong Un has said. But context and timing matters, and this opens up the opportunity for more diplomacy," said John Delury, a professor at Yonsei University's Graduate School of International Relations in Seoul.

A top North Korean diplomat at the United Nations said in October his country would not put nuclear weapons on the negotiating table "unless the hostile policy and the nuclear threat of the US is thoroughly eradicated."

Kim, the research fellow, said it was now up to negotiators to seize on the opportunity presented by the summit and potential talks with the US.

"Pyongyang's intention to denuclearize and refrain from testing during talks simply reiterates its longstanding position in principle, (they) are conditional statements and dubious, but saying them publicly nevertheless give Washington and Seoul something to work with. That's where good negotiations come in," she said.

The US and South Korea had postponed joint military exercises, which Pyongyang views as hostile, during the Winter Olympics but the drills had been expected to resume after the Paralympics end later this month. It's not clear whether Tuesday's developments will alter that.

During his Tuesday meeting, Kim told the South Korean delegation he "understands" Seoul's position on the drills.

"Our stance on the joint military drills is that it is hard to postpone the exercises again or suspend them and there is no justification for doing so. But Kim said that he understands the South's stance," an official in President Moon's administration said.