TOKYO (Reuters) – North Korea says it has resumed plutonium production by reprocessing spent fuel rods and has no plans to stop nuclear tests as long as perceived U.S. threats remain, Japan’s Kyodo news agency reported on Wednesday.

North Korea’s Atomic Energy Institute, which has jurisdiction over its main Yongbyon nuclear facilities, also told Kyodo it had been producing highly enriched uranium necessary for nuclear arms and power “as scheduled”.

“We have reprocessed spent nuclear fuel rods removed from a graphite-moderated reactor,” the institute told Kyodo in a written interview.

The institute did not mention the amount of plutonium or enriched uranium it had produced, Kyodo said.

The U.N. nuclear watchdog, the International Atomic Energy Agency (IAEA), said in June North Korea appeared to have reopened the Yongbyon plant to produce plutonium from spent fuel of a reactor central to its atomic weapons drive.

North Korea vowed in 2013 to restart all nuclear facilities, including the main reactor at its Yongbyon site that had been shut down.

North Korea had said in September that Yongbyon was operating and that it was working to improve the “quality and quantity” of its nuclear weapons.

North Korea conducted its fourth nuclear test in January.

According to Kyodo, the North Korean institute said it had already succeeded in making “lighter and diversifying” nuclear weapons, and that it had no intention of halting nuclear tests.

“Under conditions that the United States constantly threatens us with nuclear weapons, we will not discontinue nuclear tests,” the institute was quoted by Kyodo as saying.

North Korea will also build a 100,000-kilowatt light-water nuclear reactor for experimental use, the institute was quoted as saying, but it did not provide further details.

Little is known about the quantities of weapons-grade uranium or plutonium that North Korea possesses, or its ability to produce either, though plutonium from spent fuel at Yongbyon is widely believed to have been used in its nuclear bombs.

North Korea has come under tightening international pressure over its nuclear weapons program, including tougher U.N. sanctions adopted in March backed by its lone major ally China.

(Reporting by Elaine Lies; Editing by Robert Birsel)