Former Deputy Director General of the International Atomic Energy Agency (IAEA) Olli Heinonen says nuclear inspectors need to have a "robust" mandate to carry out their work in North Korea.

Heinonen said in an e-mail to Reuters on Wednesday that it is good news that the North has agreed to let IAEA inspectors go back to the Yongbyon nuclear site given that, this time, the IAEA will be provided with a real robust verification mandate.

He stressed that “a simple presence, as was the case, in particular, after the 2007 monitoring agreement, is not sufficient to ensure that North Korea is honoring its international commitments including the denuclearization of the Korean Peninsula.”

Heinonen currently is a senior fellow at Harvard University's Belfer Center for Science and International Affairs.