WASHINGTON (Reuters) – North Korea on Tuesday blew up a building set up in 2018 in a border town as a joint liaison office to foster better ties with South Korea, the latest in a series of actions by Pyongyang that have increased concerns in Washington.

North Korea’s hostilities have included missile tests and harsh rhetoric since an unprecedented summit between U.S. President Donald Trump and North Korean leader Kim Jong Un in Singapore in 2018. This has led to bouts of increased tension, though Trump – who once derided Kim as “Little Rocket Man” – has largely downplayed Pyongyang’s actions.

Here is a timeline of those developments:

June 12, 2018: The Singapore summit represented the first time a sitting American president met with a North Korean leader, but the statement that came out of the meeting was light on specifics, opting instead for general commitments.

Since the summit, North Korea has shown no tangible signs of a willingness to abandon its nuclear weapons, and experts have said it is believed to have continued development of its arsenal. Washington, at the same time, has sought to keep sanctions intact.

Feb. 28, 2019: A second summit between Trump and Kim in Vietnam collapsed over sanctions relief, raising questions about the future of denuclearization diplomacy.

Trump and Kim then met again in June on the border between North and South Korea and agreed to restart negotiations, but working-level nuclear talks in Sweden in October broke off. [nL5N26Q07P]

Dec. 3, 2019: Raising tensions at year-end, Pyongyang warned Washington of a “Christmas gift” after Kim gave the United States until 2020 to propose new concessions in nuclear talks. [nL4N28D18R] Beyond a warning from Kim that the world would soon see a “new strategic weapon,” however, the deadline passed uneventfully.

March 2020: North Korea launched a series of short-range missiles, its first such tests of the year. This drew U.S. and Chinese appeals for Pyongyang to return to talks, but there were no signs that any discussions materialized. [nL4N2B10RG]

Kim has refrained so far from resuming long-range missile launches and nuclear tests.

April/May 2020: Kim’s disappearance from public sight led to several weeks of fevered speculation about his health, fueling concerns in Washington and elsewhere about stability on the Korean Peninsula. The situation calmed in early May when state media said Kim had attended the completion of a fertilizer plant. [nL4N2CJ35B]

May 28, 2020: The U.S. Justice Department accused North Korea’s state-owned bank of evading U.S. sanctions laws and charged 28 North Korean and five Chinese citizens in its largest crackdown on North Korea sanctions violations. [nL1N2DA21T]

June 16, 2020: North Korea blew up a liaison office in Kaesong used for joint talks after threatening action if defectors continued with a campaign sending propaganda leaflets into the North. [nL4N2DT0HM]

It was a major setback to efforts by South Korean President Moon Jae-in to coax North Korea into cooperation and also appeared to be a further blow to Trump’s hopes of persuading Pyongyang to give up its nuclear weapons.