North Korean leader Kim Jong-un says his country has developed a hydrogen bomb, according to state media reports. Jong-un made the statement during an arms industry inspection on Tuesday, South Korean news agency Yonhap said, citing reports.

“The state managed to become a powerful nuclear power capable of defending its sovereignty and national dignity by mighty nuclear and hydrogen strikes,” Kim Jong-un was cited by the Korean Central News Agency (KCNA) as saying.

Kim Jong-Un noted that “the country needs to bolster its defense sector.”

Kim made the announcement during a visit to a historic military site in Pyongyang on Wednesday. He said that North Korea was a “powerful nuclear weapons state ready to detonate self-reliant A-bomb and H-bomb to reliably defend its sovereignty,” Yonhap News Agency reported.

This also marked the first time Kim has openly talked about developing hydrogen bombs, experts reportedly said.

“Kim has revealed on a number of occasions that North Korea possesses nuclear bombs. But this appears to be the first time that he talked about an H-bomb,” Chang Yong-seok, a researcher at the Seoul National University Institute for Peace and Unification Studies, told Yonhap.

A hydrogen, or thermonuclear device, uses fusion in a chain reaction that results in a far more powerful explosion.

North Korea has hinted before at the possession of “stronger, more powerful” weapons, but Kim’s remarks were believed to be the first direct reference to a hydrogen bomb.

The North has made many unverifiable claims about its nuclear weapons strength, including the ability to strike the US mainland which most experts dismiss – at least for now.

In September, the Washington-based Institute for Science and International Security had raised a red flag over what appeared to be a new “hot cell” facility under construction at the North Korea’s main Yongbyon nuclear complex. Analysts at the think-tank said satellite images suggested it could be an isotope separation facility, capable of producing tritium, a radioactive isotope of hydrogen.

However, information related to the highly secretive nation of North Korea, which has nuclear weapons, is extremely difficult to independently confirm.