Prime Minister Shinzo Abe pledged Monday to strengthen measures to ensure the safe management of nuclear materials and facilities to deter nuclear terrorism.

Japan will work closely with the International Atomic Energy Agency to achieve that goal, Abe told a plenary session of the Nuclear Security Summit attended by the leaders of nearly 60 countries, including China and South Korea, and international organizations.

"Japan will continue to endeavor domestically and internationally to strengthen nuclear security measures to advance global nonproliferation and disarmament toward abolishment of nuclear weapons," Abe told the two-day event that began Monday.

"Japan has a responsibility to take the lead in strengthening nuclear security measures," he said, referring to the fact that it is the only country to have ever come under atomic attack and is struggling to contain the 2011 crisis at the Fukushima No. 1 plant, the world's worst nuclear crisis since Chernobyl.

Abe said the government has agreed with the U.S. government to return hundreds of kilograms of highly enriched uranium and separated plutonium, which were provided for research during the Cold War era.

Abe has promoted a policy of keeping plutonium only when its use has been decided, in an apparent effort to dismiss potential concerns that Japan could go nuclear with an abundant stockpile of plutonium.

"Japan's use of atomic energy has been strictly limited to peaceful purposes and we have dealt with the issue of safeguards for a long time" in a completely transparent manner, Abe said.