WASHINGTON - North Korea has restarted a plutonium reactor that could fuel a nuclear bomb and is seeking missile technology that could threaten the United States, Washington’s top spy said Tuesday.

In an annual threat assessment, Director of National Intelligence James Clapper and senior military and intelligence officials singled out the authoritarian pariah state as a major and unpredictable menace. Lieutenant General Vincent Stewart, the director the the Defense Intelligence Agency, joined Clapper to brief the Senate Armed Services Committee on the global dangers faced by US planners.

“North Korea’s nuclear weapons program and evolving missile programs are a continuing threat,” he said. Clapper said the Kim’s Pyongyang regime continues to develop cyber-espionage capabilities, and has sold illegal weapons technology to other states. Last month, the regime tested what it said was a “hydrogen bomb,” but US intelligence believes “the yield was too low for it to have been successful test of a staged thermonuclear device.”

It was the north’s fourth nuclear test, and an apparent bid to expand its arsenal with a more destructive thermonuclear device. Despite this apparent failure, North Korea has pressed on with its ballistic missile program and on Saturday launched a rocket into space, a move which Washington and Tokyo said was a banned weapons test.

“Pyongyang continues to produce fissile material and develop a submarine launched ballistic missile,” Clapper told the lawmakers. “It is also committed to developing a long-range nuclear-armed missile that’s capable of posing a direct threat to the United States, although the system has not been flight tested.” Perhaps most worrying for the Americans, however, is North Korea’s resumption of plutonium production — a sign it remains bent on producing a more powerful bomb despite international economic sanctions.