North Korea says it has successfully tested an engine designed foran intercontinental ballistic missile.
The new type of engine would "guarantee" the ability to launch a nuclear strike on the US mainland, the KCNA news agency said.
The test was conducted at the country's long-range missile launch site near its west coast.
It is the latest in a series of tests and launches carried out by the isolated nation.
Leader Kim Jong-un supervised the test, state media report, during which "the engine spewed out huge flames with a deafening boom".
The country would now be able to "keep any cesspool of evils in the earth including the US mainland within our striking range," Mr Kim was quoted as saying.
North Korea should "refrain from actions and rhetoric that further destabilise the region and focus instead on taking concrete steps toward fulfilling its commitments and international obligations," said US state department spokesman Mark Toner.