The chief of the International Atomic Energy Agency (IAEA) has urged North Korea to come clean on its nuclear programs.

In his annual speech to the U.N. General Assembly Monday, IAEA Director General Mohamed ElBaradei, said that North Korea continued "to pose a serious challenge to the nuclear nonproliferation regime," stressing that the body's inspectors must be allowed back into the country.

He called on North Korea to rejoin the Nuclear Non-Proliferation Treaty that it left two years ago.

The head of the U.N. nuclear watchdog said he was "frustrated" that Pyongyang was refusing to take part in six-party talks on settling its nuclear standoff.

He said the international community would be ready to respond to the North Koreans' economic and humanitarian needs, quickly adding however that "a prerequisite is for Pyongyang to commit itself to a full, verifiable dismantlement of its weapons program."
ElBaradei said that even if the project were not to be dismantled, North Korea should still allow a comprehensive verification by the IAEA to confirm that the North's program is exclusively peaceful in nature.

ElBaradei's remarks come as a team of IAEA inspectors are in Seoul to conduct a third round of inspections on South Korea's past nuclear activities.