Tokyo-North Korea, which mothballed the Yongbyon reactor in 2007 under an aid-for-disarmament accord, began renovating it after its third nuclear test in 2013.

Pyongyang carried out a fourth test on January 6, leading to tension in the region.

In June, the U.N.’s atomic watchdog warned that North Korea could have reactivated the Yongbyon plant for reprocessing plutonium for use in nuclear weapons, following similar warnings from a U.S. think tank.

The North’s Atomic Energy Institute, which has jurisdiction over the country’s main atomic complex Yongbyon, told Kyodo News on Wednesday that it had been producing highly enriched uranium for nuclear arms and power “as scheduled.”

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

The agency did not disclose how much plutonium or enriched uranium the North has produced, Kyodo said.

The type of plutonium suitable for a nuclear bomb typically needs to be extracted from spent nuclear reactor.

The North’s Atomic Energy Institute did not rule out the possibility of further nuclear tests, claiming it had had success in “minimizing, making lighter and diversifying” nuclear weapons, Kyodo said.

“Under conditions that the United States constantly threatens us with nuclear weapons, we will not discontinue nuclear tests,” the institute said, according to Kyodo.

Meanwhile, South Korea said Wednesday that North Korea’s deputy ambassador to Britain had defected to Seoul, in a rare and damaging loss of diplomatic face for Pyongyang.

The Unification Ministry said Thae Yong-Ho — the number-two at the North’s mission in London — had defected together with his family and they were now in the South Korean capital.

“They are under government protection and are going through necessary procedures with related institutions,” ministry spokesman Jeong Joon-Hee told reporters.

An official at the North Korean embassy in London would not confirm the defection on Tuesday, describing reports of the event as “quite sudden.”

“If it is appropriate to give a response, then you might hear about our response,” the official told Reuters.