The leader of North Korea is reportedly claiming the country now has the ability to detonate a powerful hydrogen bomb, though his comments immediately drew skepticism from experts.

The state-run KCNA news agency reported Thursday that Kim Jong-un made the announcement while at the Phyongchon Revolutionary Site, which is significant to the country’s arms history.

According to the KCNA report, Kim said North Korea had evolved into “a powerful nuclear weapons state ready to detonate self-reliant A-bomb and H-bomb to reliably defend its sovereignty and the dignity of the nation.” If true, it would be a landmark development.

Hydrogen bombs rely on a different nuclear reaction than atomic bombs and are known to be much more powerful. South Korea’s Yonhap news agency reported that while Kim has publicly touted on numerous occasions that his country has atomic-bomb capabilities, this appeared to be the first time the leader publicly indicated that North Korea possessed a hydrogen bomb.

Still, experts took Kim’s claim with a grain of salt. The leader is known for making bold claims.

“It’s hard to regard North Korea as possessing an H-bomb. I think it seems to be developing it,” Lee Chun-geun, a research fellow at the Science and Technology Policy Institute, told Yonhap.

The BBC quoted John Nilsson-Wright, the head of the Asia Program at Britain’s Royal Institute of International Affairs, as saying Kim’s comments appeared to be “an attention-grabbing effort to assert North Korean autonomy and his own political authority.”