This undated picture released from North Korea's official Korean Central News Agency (KCNA) on May 5, 2017 shows North Korean leader Kim Jong-Un inspecting the defence detachment on Jangjae Islet and the Hero Defence Detachment on Mu Islet.

WASHINGTON — North Korea, the only nation to test nuclear weapons this century, spent most of President Donald Trump's first year in office tuning up its nuclear arsenal.

Under third-generation North Korean leader Kim Jong Un, the reclusive state has conducted its most powerful nuclear test, launched its first-ever intercontinental ballistic missile and threatened to send missiles into the waters near Guam.

Last week, the world braced for Kim's "Christmas gift" to the United States, a promise the reclusive leader made if the Trump administration did not work to salvage stalemated nuclear negotiations. Trump downplayed Kim's cryptic message and said that the — rather than a missile test.

"Maybe it's a nice present. Maybe it's a present where he sends me a beautiful vase as opposed to a missile test," Trump said. "I may get a vase. I may get a nice present from him. You don't know. You never know."

And although Kim's Christmas gift did not manifest, the North's state-run media said earlier this year that a "very important" test was carried out at a rocket testing ground. Trump responded to the report by tweeting that .

"Kim Jong Un is too smart and has far too much to lose, everything actually, if he acts in a hostile way. He signed a strong Denuclearization Agreement with me in Singapore," Trump wrote on Twitter, referring to his historic summit with Kim in 2018.

On the heels of the test, North Korea's ambassador to the United Nations said and lengthy talks with Washington were no longer needed.

Since 2011, Kim has launched more than 100 missiles and conducted four nuclear weapons tests, which is more than what his father, Kim Jong Il, and grandfather, Kim Il Sung, launched over a period of 27 years.