International Atomic Energy Agency (IAEA) chief Yukiya Amano said that satellite imagery of North Korea's nuclear sites indicated that the country was expanding its atomic program. The head of the UN's atomic energy agency spoke on Monday at the opening of a 35-nation board meeting of the IAEA.

"Since my last report, we have observed renovation and construction activities at various locations," Amano told the IAEA's governing board, referring in particular to the Yongbyon nuclear complex.

Yongbyon facility flagged as main cause of concern

The building was believed to house uranium enrichment centrifuges, which could make bomb fuel. Amano reported that it had doubled in size, adding that the operation status of that facility was unknown.

North Korea has carried out various nuclear tests and missile drills in the past

The Yongbyon site also includes a smaller reactor and a larger one under construction. The IAEA's satellite observation indicated that an electrical switchyard had been built next to the larger reactor, while major technical components had yet to be installed in the reactor itself.

The UN's nuclear agency also detected activities that were apparently related to uranium mining and milling at the Pyongsan uranium mine.

No end in sight to diplomatic standoff

North Korea has so far conducted three nuclear explosion tests. A military spokesman had declared in May that the country had succeeded in developing small atomic explosive devices, a key step toward arming missiles with warheads.

The agency is trying to keep tabs on North Korea, where it has had no presence since the country told its inspectors to leave after withdrawing from the Nuclear Nonproliferation Treaty 12 years ago.

Following Iran's recent nuclear deal with world powers in July, Pyongyang's Foreign Ministry said that it was not interested in negotiating a similar agreement to freeze or scale down its own nuclear program.

ss/jil(AP, dpa)