North Korea confirmed the production of plutonium has been restarted in the country after speculations that it reopened its Yongbyon nuclear facility earlier this month, Japan’s Kyodo news agency reported Wednesday. Pyongyang also said it will continue conducting nuclear tests till perceived threats from U.S. remain.

“We have reprocessed spent nuclear fuel rods removed from a graphite-moderated reactor,” the Atomic Energy Institute, which has jurisdiction over the reclusive state’s main nuclear facilities at the Yongbyon complex, said in a written interview with Kyodo News. Pyongyang had also been manufacturing highly enriched uranium required for nuclear arms and power “as scheduled,” the Institute added.

The Yongbyon reactor was closed down in July 2007. However, North Korean government officials said in September 2015 that the plant was operational again, adding it was working on improving the “quality and quantity” of its nuclear weapons. Since then, the Kim Jong Un-led country has carried out several nuclear and missile tests, eliciting stricter sanctions from the United Nations Security Council.

The amount of weapons-grade uranium and plutonium that North Korea holds remains unclear. Reports say that the plutonium produced at the Yongbyon facility is used in the country’s nuclear bombs.