South Korea's unification ministry on Tuesday called on North Korea to abide by agreements it has made with the international community for the denuclearization of the Korean Peninsula amid reports the reclusive regime is continuing activities at its main Yongbyon nuclear complex.

On Monday, Rafael Grossi, director general of the International Atomic Energy Agency (IAEA), said the agency's monitoring team has spotted indications of activity at the 5-megawatt reactor at the complex north of Pyongyang, calling the move "deeply regrettable."

"The government, in close coordination with related countries and agencies, such as the United States and the IAEA, is continuing the monitoring of North Korea's nuclear and missile activities," a ministry official told reporters on background.

The official declined to comment further on "intelligence matters" but added there hasn't been any major activities worthy of attention.

"(We) urge North Korea to respect the spirits of agreements it has signed with the international community and South Korea (to push for the complete denuclearization of the Korean Peninsula)," the official said.

According to the UN nuclear watchdog, the North appears to be building an annex to a centrifuge enrichment facility at Yongbyon, though its purpose has yet to be determined. (Yonhap)