SEOUL, Jan 6 (Reuters) - North Korea said it successfully tested a miniaturized hydrogen nuclear device on Wednesday, claiming a significant advance in the isolated state's strike capability and setting off alarm bells in Japan and South Korea.
The test, the fourth time North Korea has exploded a nuclear device, was ordered by young leader Kim Jong Un, state media said.
"Let the world look up to the strong, self-reliant nuclear-armed state," Kim wrote in what North Korean state TV displayed as a handwritten note.
The announcement on North Korean state TV followed detection of a 5.1 magnitude earthquake near its known nuclear test site earlier. The state claims the test was done in "self defense against the U.S. having numerous and humongous nuclear weapons."
The reported nuclear test drew condemnation abroad, including from China and Russia, North Korea's two main allies. China expressed "resolute opposition" and said it would lodge a protest with Pyongyang.
The White House, while it could not yet verify the success of the nuclear test, quickly condemned Pyongyang's violation of international law and promised to defend its South Korean ally.
"We have consistently made clear that we will not accept it as a nuclear state," a White House spokesperson said in a statement.
