The head of the International Atomic Energy Agency expressed serious concern that North Korea may be preparing for a nuclear test.

Director-General Rafael Grossi is attending a closed IAEA Board of Governors session that opened Monday in Vienna.

The UN nuclear watchdog has released Grossi's introductory statement. Grossi said one of the tunnel entrances at the nuclear test site at Punggye-ri, North Korea, has been reopened, possibly in preparation for a nuclear test.

He also commented on Ukraine's Zaporizhzhia nuclear power plant. The plant remains under the control of Russian forces there.

He said the Ukrainian regulator has told the IAEA that they have "lost control over" the facility's nuclear material.

He said the situation there is a clear and present risk to the safety, security and safeguards at the plant.

He said the IAEA is working on how to send a team of international experts to the plant to ensure safety there.