The head of the International Atomic Energy Agency(IAEA) has said that North Korea appears to be test-running the light water reactor at its key nuclear complex in Yongbyon.

IAEA Director General Rafael Grossi presented the assessment in his opening remarks for the agency’s board of governors meeting in Vienna, Austria on Wednesday, citing a strong outflow of water observed from the reactor’s cooling system since mid-October.

Grossi said that these observations are consistent with the commissioning of the reactor, long suspected to be a facility for increasing the production of nuclear materials used to manufacture nuclear warheads.

He also noted indications of continuous activity at the Yongbyon facilities, such as the five-megawatt reactor, the reported centrifuge enrichment facility and its annex.

The IAEA chief said that the North's Punggye-ri nuclear test site remains prepared to support a new test, calling the regime’s nuclear activity “very regrettable” and a clear violation of the UN Security Council resolutions.

Grossi urged Pyongyang to cooperate with the IAEA in the full and effective implementation of its Nonproliferation Treaty Safeguards Agreement.