North Korea said Sunday that it carried out a "very important test" at its rebuilt Sohae satellite launch site that had been put out of commission due to nuclear negotiations with the United States. The move comes after North Korea's U.N. ambassador said that "denuclearization is already gone out of the negotiation table." 

Some analysts believe that the test could be preparation for the launch of an intercontinental ballistic missile (ICBM). North Korea has recently threatened Japan with an ICBM after Pyongyang conducted rocket launches last month.

Earlier this week, President Trump said that North Korean leader Kim Jong Un "likes sending rockets up, doesn't he?" in reference to Kim's recent rocket launches. 

"That's why I call him Rocket Man," Trump added. The "Rocket Man" name angered Pyongyang, with a North Korean government official saying that if Trump does it again, he will "again show the senility of a dotard." 

North Korea has set a year-end deadline for a nuclear deal with the United States, with North Korea hoping to be relieved of the burdensome sanctions imposed on the isolated Asian country. North Korean and U.S. negotiators last met in Sweden in October, but diplomatic talks fell through on the first day of discussions.

President Trump has had an unusually friendly relationship with Kim, with the two leaders meeting in Vietnam and Singapore for nuclear negotiations. Although no nuclear deal has been achieved, it could be considered a breakthrough in the normally icy relationship between Washington and Pyongyang. 

Trump and Kim's relationship started off in a rough fashion, with Trump mocking Kim in front of the U.N. in September 2017 and Kim calling Trump a "mentally deranged."