Obama offers dire warning of possible nuclear attack launched by terrorists

Groups like al Qaeda are working hard to acquire nuclear weapons, and "if they ever succeed, they would surely use it," President Barack Obama said while speaking to more than 40 world leaders Tuesday.

Obama, addressing the opening plenary session of the nuclear security summit in Washington, asked his foreign counterparts to join together "not simply to talk, but to act."

The president's summit has already yielded early successes for the administration with Monday's announcement that Ukraine will give up its stockpiles of highly enriched uranium and China's promise to work with the U.S. on a sanctions resolution on Iran.

On Tuesday, Obama opened with the focus of the summit, building an international effort to prevent loose nuclear material from ending up in the hands of terrorists.

Obama said that 20 years after the end of the Cold War, the world faces "a cruel irony": that the risk of "a nuclear confrontation between nations has gone down, but the risk of a nuclear attack has gone up."

"Nuclear materials that could be sold or stolen and fashioned into a nuclear weapon exist in dozens of nations," Obama said in excerpts released by the White House. "Just the smallest amount of plutonium — about the size of an apple — could kill and injure hundreds of thousands of innocent people."

Obama warned that if al Qaeda or other extremist groups were able to successfully use a nuclear device, it "would be a catastrophe for the world — causing extraordinary loss of life and striking a major blow at global peace and stability."

The president called the summit an opportunity to do more than talk, but to coalesce around an international effort of action.

"Not simply to make pledges, but to make real progress for the security of our people," Obama said. "All this, in turn, requires something else, something more fundamental. It requires a new mindset — that we summon the will, as nations, as partners, to do what this moment in history demands."