The U.N. head sent a strong message from his office Monday to delegates gathered in Vienna for the 57th general conference of the International Atomic Energy Agency.
"I remain deeply concerned about the risks posed by nuclear proliferation," Ban said in a statement. "I call upon the Democratic People's Republic of Korea to demonstrate its commitment towards a verifiable denuclearization. I also call upon the Islamic Republic of Iran to fulfill its pledge to enhance the transparency of its nuclear program.
IAEA Director General Yukiya Amano told delegates there has been progress on the nuclear security front, though lingering concerns remained over North Korea's weapons program and Iran's nuclear intent.
North Korea last week restarted an enrichment reactor nearly seven months after conducting an underground nuclear test, its third. The IAEA said in a recent report there may be a military dimension to Iran's nuclear program, an allegation the government denies.
Both programs have been the subject of long-term international negotiations.
Amano was appointed to a second four-year term as director general during the conference in Vienna.