On New Year's Day of this year, North Korean leader Kim Jong-un said his country was getting ready to test an intercontinental ballistic missile, which would have the range to strike the U.S. North Korea also says it can produce a nuclear weapon small enough to fit on an ICBM, though none of its claims have been verified.
A North Korean military unit tasked with striking U.S. bases in Japan was involved in those launches, the state news agency said.
This image aired on the North's Chosun Central TV shows a ground rocket engine test under way at the Sohae Satellite Launching Ground on March 18, 2017.
Kim, who personally supervised the test, said that "the whole world will soon witness what eventful significance the great victory won today carries", according to KCNA.
North Korean news agencies reported last night (Saturday) that a new type of high-thrust rocket engine has been tested.
"We do not want to interfere in (other country's) political matters, but it is our responsibility to investigate a murder case which occurred within our jurisdiction".
In Seoul, Mr Tillerson laid out details of the new USA plan, saying it would focus on getting China to better enforce United Nations sanctions against North Korea.
It said the test was meant to confirm the engine's thrust power and gauge the reliability of its control system and structural safety.
"Some of these technologies which the North Koreans are including in their rocket expansion program actually have to do with a covert method of firing missiles without being detected in advance of actually exploding the devices".
North Korea has stepped up its efforts to develop a nuclear-tipped missile that could reach the USA mainland, although experts are divided on how close it is to reaching its stated goal.
Trump made the comments to reporters while departing his Mar-a-Lago resort in Florida, where he spent the weekend.
North Korea's watchdog, 38 North, said the deeper the tunnel goes beneath Mount Mantap, the bigger the blast which can be contained there during testing.
During his visit to Seoul, Tillerson admitted that Washington's "strategic patience" policy toward Pyongyang was over.
USA president Donald Trump's new right hand man Rex Tillerson met with his Chinese counterpart on Saturday. They have been "playing" the United States for years.