North Korea has run its nuclear reactor for long enough to harvest plutonium "within a matter of weeks to months" and Pyongyang is also believed to have taken "initial steps" toward fielding a road-mobile intercontinental ballistic missile, the U.S. intelligence chief said Tuesday.

Director of National Intelligence James Clapper unveiled the assessment in his "Worldwide Threat Assessment" report submitted to the Senate Armed Services Committee, days after North Korea carried out a banned missile launch following its fourth nuclear test a month earlier.

Clapper said the North has followed through on its 2013 announcement to "refurbish and restart" its nuclear facilities, including the uranium enrichment facility and its five-megawatt reactor at its Yongbyon nuclear complex.

"We further assess that North Korea has been operating the reactor long enough so that it could begin to recover plutonium from the reactor's spent fuel within a matter of weeks to months," he said. 

The graphite-moderated reactor has been the source of weapons-grade plutonium for the communist nation. The small reactor is capable of producing spent fuel rods that, if reprocessed, could give the regime enough plutonium to make one bomb a year.

The reactor has provided Pyongyang with weapons-grade plutonium that the regime used in its first three nuclear tests, in 2006, 2009 and 2013. The North conducted its fourth nuclear test on Jan. 6, claiming it successfully detonated a hydrogen bomb.

Clapper expressed skepticism about the North's H-bomb claims, saying, "The low yield of the test is not consistent with a successful test of a thermonuclear device."

Speaking of the North's missile program, the intelligence chief said that Pyongyang is also committed to developing "a long-range, nuclear-armed missile that is capable of posing a direct threat" to the U.S., and has publicly displayed its KN-08 road-mobile intercontinental ballistic missile on many occasions.

"We assess that North Korea has already taken initial steps toward fielding this system, although the system has not been flight-tested," Clapper said without elaborating.

The KN-08 is believed to have a range of at least 5,500 km, which puts Alaska at risk. U.S. officials have expressed concern about the missile in that it can be launched from elusive mobile platforms.

Deputy Defense Secretary Robert Work also voiced concern about the KN-08 missile later in the day.

The North is "committed to developing long-range nuclear armed missiles such as the KN-O8, which could pose a direct threat to the continental United States if it is successfully designed and fielded. That is a new thing," Work said during a Pentagon briefing on the defense budget for next year.

Work also said the North is "already a nuclear-armed regional power."

"Moreover, another new thing is that the new leader, Kim Jong-un, has demonstrated a propensity for provocation, which lends itself to miscalculation and is very, very, in our view, destabilizing and risky," he said.

Clapper also noted the North claimed in May that it successfully tested a ballistic missile from a submarine, but he didn't give an assessment on that.

"Although North Korea issues official statements that include its justification for building nuclear weapons and threats to use them as a defensive or retaliatory measure, we do not know the details of Pyongyang's nuclear doctrine or employment concepts," Clapper said.

"We have long assessed that Pyongyang's nuclear capabilities are intended for deterrence, international prestige, and coercive diplomacy," he said.

Clapper said North Korean leader Kim Jong-un has further solidified his position as the "unitary leader and final decision authority through purges, executions, and leadership shuffles" since taking over the communist nation in late 2011.

Kim and his regime have also publicly emphasized -- and codified -- the North's focus on advancing its nuclear weapons program, developing the country's troubled economy, and improving the livelihood of the North Korean people, while maintaining the tenets of a government-run, "command economy," the intelligence chief said.

"Despite efforts at diplomatic outreach, Kim continues to challenge the international community with provocative and threatening behavior in pursuit of his goals, as prominently demonstrated in the November 2014 cyber-attack on Sony, the August 2015 inter-Korean confrontation spurred by the North's placement of landmines that injured two South Korean soldiers, and the fourth nuclear test in January 2016," he said.

Asked for comment on Clapper's assessment of the North's nuclear and missile capabilities, State Department spokesman John Kirby said that the assessment "underscores to us the very strong sense of urgency that we have here at the State Department to see that the North is held to account and that tougher measures are put in place through the international community." (Yonhap)