North Korean leader Kim Jong Un's threat to show the world a new strategic weapon and possibly resume long-range missile tests is another dramatic turn in his high-stakes summitry with President Donald Trump. Some key moments in North Korea-U.S. diplomacy:

Jan. 1, 2018: Kim uses his annual New Year's address to call for improved relations with South Korea though adds that he has a nuclear button on his desk. Trump tweets that he has a bigger and more powerful nuclear button, adding ``and my Button works!''

March 5-6, 2018: South Korean presidential envoys meet with Kim in Pyongyang and report he is willing to discuss his nuclear program with the United States.

March 8, 2018: South Korean envoys meet Trump at the White House and deliver an invitation from Kim to meet with Trump, who accepts.

April 21, 2018: North Korea unilaterally suspends its nuclear and ICBM tests and says it will shift its focus to developing its economy. Trump tweets: ``This is very good news for North Korea and the World.''

April 27, 2018: Kim holds a summit with South Korean President Moon Jae-in. The leaders make vague vows for denuclearization and peace.

May 9, 2018: U.S. Secretary of State Mike Pompeo visits Pyongyang to prepare for a Trump-Kim summit. North Korea releases three Americans who had been imprisoned.

June 12, 2018: Trump and Kim meet in Singapore for the first summit between the countries' leaders since the end of the 1950-53 Korean War. They issue an aspirational statement on a nuclear-free Korean Peninsula without describing when and how it would occur.

Jan. 1, 2019: Kim in his New Year's Day speech says he hopes to continue his nuclear summitry with Trump but also that he would seek a ``new way'' if the United States persists with sanctions and pressure against the North.

Feb. 27-28, 2019: Trump and Kim meet in Hanoi, Vietnam, for their second summit. The meeting breaks down after the Americans reject North Korean demands for major sanctions relief in exchange for a partial surrender of its nuclear capabilities.

April 13, 2019: Kim sets the year's end as a deadline for the Trump administration to offer mutually acceptable terms for an agreement to salvage the diplomacy.

May 9, 2019: North Korea fires two short-range missiles toward the sea in its second launch in five days, ending a pause in ballistic testing and ramping up pressure on Washington over the slow pace in negotiations.

June 30, 2019: Trump holds an impromptu summit with Kim at the inter-Korean border and becomes the first U.S. president to cross over into North Korean territory. The leaders agree to resume working-level talks.

Oct. 3, 2019: North Korea says it carried out its first underwater-launched ballistic missile test in three years. The missile, which possibly could be launched from a submarine, represents the North's most high-profile weapons test since the start of diplomacy in 2018.

Oct. 10, 2019: North Korea threatens to resume nuclear and ICBM tests days after the collapse of the working-level talks in Sweden, which North Korean officials blamed on the Americans' ``old stance and attitude.''

Dec. 3, 2019: North Korea says the Trump administration is running out of time to salvage nuclear negotiations, saying it's entirely up to the United States to choose what ``Christmas gift'' it gets from the North.

Dec. 7, 2019: North Korea says it performed ``a very important test'' at its long-range rocket launch site. Six days later, North Korea says it conducted ``another crucial test'' at the same site, prompting speculation that it's developing a new ICBM or preparing a satellite launch.

Jan. 1, 2020: North Korea says Kim during a key political conference accused the Trump administration of dragging its feet in nuclear negotiations and warned that his country will soon show a new strategic weapon that would bolster its nuclear deterrent in the face of ``gangster-like'' U.S. pressure. Kim also says the North would no longer be bound to its moratorium on nuclear and ICBM tests.