The director of the UN’s nuclear watchdog said on Friday that North Korea’s sixth nuclear test on September 3 showed significant progress, but declined to say whether Pyongyang had tested a hydrogen bomb.

International Atomic Energy Agency (IAEA) Director General Yukiya Amano made the comment after a bilateral meeting with South Korean foreign minister Kang Kyung-hwa on Friday morning in Seoul.

Pyongyang on September 3 claimed that it had tested “a hydrogen bomb” which could be mounted on an intercontinental ballistic missile (ICBM), describing the test as the “perfect success.”

The IAEA chief, however, said the agency could not judge whether it was