Donald Trump and Kim Jong Un: A timeline of events

From "Little Rocket Man" to an apparent thawing of relations, here's a look back at major milestones in the United States' relationship with North Korea and its leader Kim Jong Un since President Donald Trump took office.

2017

The first year of Trump's presidency was marked by a heated back-and-forth as North Korea tested more than a dozen missiles, prompting Trump to respond, often on Twitter. Trump famously referred to Kim as "Little Rocket Man" at various times both on and off the internet.

Swelling tensions reached a new high on Aug. 9, 2017, as North Korea threatened a strike on the U.S. territory of Guam in a statement distributed by its state-run news agency. The country said its military was reviewing a plan to create an "enveloping fire" around Guam, 2,100 miles from North Korea.

Icy relations and missile tests continued, with North Korea claiming in late November that it had a nuclear-capable intercontinental ballistic missile that could reach the entire continental U.S.

2018

But things began to change in 2018 amid an apparent larger shift in North Korean foreign policy. These are some of the key events from 2018 so far:

March 7: A top South Korean official visits Pyongyang and says Kim is willing to discuss the fate of his nuclear arsenal with the United States and expressed a readiness to suspend nuclear and missile tests during such talks.

March 9: Trump accepts Kim's invitation to meet, which White House initially says will take place by the end of May.

March 27: Kim makes a surprise visit to Beijing and meets Chinese President Xi Jinping in an apparent move to strengthen his leverage ahead of negotiations with Trump.

April 18: Trump confirms that Mike Pompeo, then the CIA chief, had met secretly with Kim in North Korea and said "a good relationship was formed" heading into the adversaries' anticipated summit.

April 21: North Korea says it has suspended nuclear and long-range missile tests and plans to close its nuclear test site as part of a shift in its national focus to improving the economy. Trump tweeted, "This is very good news for North Korea and the World" and "big progress!"

May 9: Pompeo, now U.S. secretary of state, makes an unannounced one-day trip to Pyongyang to prepare for the planned Trump-Kim summit. North Korea releases three Americans who had been imprisoned, and they return with Pompeo to the U.S.

VIDEO: Who are the detainees released by North Korea?

May 10: Trump announces he will meet with Kim in Singapore on June 12. He tweets: "We will both try to make it a very special moment for World Peace!"

May 12: North Korea says it will hold a ceremony to dismantle its nuclear test site between May 23 and 25 and foreign journalists will be invited to attend.

May 24: Trump calls off the planned summit, calling the cancellation a "tremendous setback" for peace and stressing that the US military was ready to respond to any "foolish or reckless acts" by the North.

June 1: Trump announced that his historic summit with Kim is back on for June 12 in Singapore. Trump made the announcement, just a week after he canceled the summit, after an hour-long meeting with a top North Korean official who delivered a letter from the North Korean leader.

The Associated Press and ABC News contributed to this report.