It has conducted five nuclear tests since 2006 - three under Kim Jong-Un - and launched a number of missiles as it seeks to develop a weapon capable of reaching the U.S. mainland. "We will follow the legal channel to get them", he said.
South Korea's military acknowledged Monday that the test, which apparently was conducted on Saturday, showed the North was developing a more sophisticated engine.
Claiming the test to be successful, Kim Jong-un said it was a new birth of the nation's rocket industry.
Kim Jong Un attended the ground test of a new type high-thrust rocket engine at the Sohae launch site Sunday, as US Secretary of State Rex Tillerson met with Chinese President Xi Jinping in Beijing.
Kim attended the test at the Sohae launch site, according to a report on Sunday by the Korean Central News Agency, which said the test was meant to confirm the "new type" engine's thrust power and gauge the reliability of its control system and structural safety.
North Korea is banned by the United Nations from conducting long-range missile tests, but it claims its satellite program is for peaceful use, a claim many in the USA and elsewhere believe is questionable. That would put parts of the United States in range.
Ford recalls 440K vehicles for fire risk, door latch trouble
That can lead to a crack in the cylinder head, which could lead to a pressurized oil leak and that could result in an engine fire. Driving a auto that is on fire or that has doors popping open is impressive, but not recommended.
Earlier this month, it fired off four ballistic missiles into the Sea of Japan, reportedly reaching within 200km of Japan's shoreline. The simultaneous firings appeared created to outsmart the Terminal High Altitude Area Defense antimissile battery that the United States is deploying to South Korea, which would have difficulty shooting down four targets at once. It was developed without "dependence on the technology of other countries", KCNA said.
"This was a comprehensive test for the first-stage rocket for an ICBM, and that is why it was unsafe", said Kim Dong-yub, an analyst at Seoul's Institute for Far Eastern Studies. They have been "playing" the United States for years. "We hope all parties, including our friends from the United States, could size up the situation in a coolheaded and comprehensive fashion and arrive at a wise decision". After the test last April, North Korea's rhetoric was much more intense.
North Korea has become an global pariah as it attempts to manufacture nuclear weapons.
"What could be next is they would make a new type of ICBM with this new engine system and launch it, but not the entire stages, but to make only the first stage, fly about 400 km and drop", Kim explained, "They are not going to show it all at once".
Trump looks forward to "the opportunity of a visit in the future", Tillerson said, in an apparent reference to unconfirmed reports of plans for the two leaders to meet in Florida next month.