The head of the International Atomic Energy Agency says North Korea's fifth nuclear test is a "clear violation" of United Nations Security Council resolutions.

Yukiya Amano, opening the IAEA board of governors meeting in Vienna on Monday, called for North Korea to allow the return of inspectors, who were last there in April 2009.

He says "we keep on training them, updating the verification plan, and we can send them back in short notice."

He would not comment on U.S. Secretary of State John Kerry's call for North Korea to freeze its nuclear and missile plans immediately, but called North Korea's test earlier this month "deeply troubling and regrettable."

He says "these activities of nuclear testing and launches of missiles are a serious threat to northeast Asia and beyond."