The chief of the International Atomic Energy Agency(IAEA) said that there are signs of activities at North Korea's Yongbyon nuclear complex, calling them "deeply regrettable."

Speaking to the IAEA Board of Governors on Monday, Director General Rafael Grossi said that the nuclear watchdog has continued to monitor the North's nuclear program since last August, and spotted indications of activity at the five-megawatt reactor in the nuclear complex.

Grossi said there are ongoing indications of activity at the Kangson uranium enrichment complex and the Pyongsan uranium mine and concentration plant as well.

The IAEA chief, however, said that there were no signs of activity at the radiochemical laboratory at Yongbyon, a facility where plutonium is extracted by reprocessing spent fuel rods removed from reactors.

Gross said the continuation of the North's nuclear program is a clear violation of relevant UN Security Council resolutions and is deeply regrettable.