Director of National Intelligence James Clapper said that Pyongyang announced in 2013 its intention to refurbish and restart nuclear facilities, to include the uranium enrichment facility at Yongbyon and its graphite-moderated plutonium production reactor, which was shut down in 2007.
"We assess that North Korea has followed through on its announcement by expanding its Yongbyon enrichment facility and restarting the plutonium production reactor," Clapper said in an opening statement to the Senate Armed Services Committee.
Clapper also said that Islamic militants will continue plotting against US interests overseas and homegrown attacks will pose the most significant threat from violent extremists to Americans at home.
"The perceived success of attacks by homegrown violent extremists in Europe and North America, such as those in Chattanooga and San Bernardino, might motivate others to replicate opportunistic attacks with little or no warning, diminishing our ability to detect terrorist operational planning and readiness," he said.
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Clapper also said Iran remains the top state sponsor of terrorism, al-Qaeda-linked groups remain resilient and the US will continue to see cyber threats from China, Russia and North Korea.
Clapper said US information systems, controlled by the US government and American industry, are vulnerable to cyberattacks from Russia and China. North Korea "probably remains capable and willing to launch disruptive or destructive cyberattacks to support its political objectives," he said.
Russia's cyber operations are likely to target US interests in part to underpin its intelligence gathering to support Russia's moves in the Ukraine and Syrian crises, he said.