A Senior State department official confirmed on Tuesday that North Korea is re-starting its plutonium production program "in defiance" of international sanctions.

The U.S. assessment came a day after the U.N. nuclear watchdog said it had “indications” that Pyongyang has reactivated a plant to recover plutonium from spent reactor fuel at Yongbyon, its main nuclear complex.

The latest developments suggest North Korea’s reclusive communist government is working to ensure a steady supply of materials for its drive to build warheads, despite tightened international sanctions after its fourth nuclear test in January.

The official spoke on the condition of anonymity and said that Washington is worried by the new effort.

“Everything in North Korea is a cause for concern,” the official told Reuters.

“They take the spent fuel from the 5 megawatt reactor at Yongbyon and let it cool and then take it to the reprocessing facility, and that’s where they’ve obtained the plutonium for their previous nuclear tests. So they are repeating that process,” the official said. “That’s what they’re doing.”

International Atomic Energy Agency (IAEA) said last year that it had noticed signs North Korea was resuming activity at Yongbyon.

IAEA chief Yukiya Amano told a news conference in Vienna on Monday that there have been indications of renewed plutonium reprocessing activities at Yongbyon. Reprocessing involves extracting plutonium from spent reactor fuel, one route to obtaining bomb fuel other than uranium enrichment.

“I would agree that there are indications,” the U.S. official said.

But no need to worry. As TruthRevolt reported yesterday, John Kerry is confident that he can defuse the threat of a nuclear North Korea the same way he defused the threat of a nuclear Iran - with an agreement that encourages North Korea's nuclear ambitions.