President Barack Obama meets with Russian President Dmitry Medvedev.

The leaders of the world's two greatest nuclear powers have agreed to reduce their nations' nuclear arsenals. U.S. President Barack Obama and Russian President Dmitry Medvedev have signed a "joint understanding" to reduce their countries' nuclear warheads and the means to deliver them by up to a third of current levels. A legally binding treaty is to be completed within the year. The new treaty will replace the 1991 Strategic Arms Reduction Treaty, known as START, which expires December 5, 2009.

The leaders also agreed on a joint statement on nuclear security cooperation that will help achieve the goal of securing all vulnerable nuclear materials within 4 years.

President Obama said it is important that the U.S. and Russia lead by example in stopping the spread of nuclear weapons and preventing their use:

"The notion that prestige comes from holding these weapons, or that we can protect ourselves by picking and choosing which nation can have these weapons, is an illusion. In the short period since the end of the Cold War, we've already seen India, Pakistan, and North Korea conduct nuclear tests. Without a fundamental change, do any of us truly believe that the next two decades will not bring about the further spread of these nuclear weapons?"

President Obama said America is committed to stopping nuclear proliferation and is ultimately seeking a world without nuclear weapons. The U.S. - Russian agreements to reduce nuclear arsenals and to work together to secure nuclear materials are significant steps toward achieving these critical goals.

As the U.S. and Russia keep their nuclear commitments, it is also important, said the President, that other nations be held accountable for meeting their obligations:

"That's why we should be united in opposing North Korea's efforts to become a nuclear power, and opposing Iran's efforts to acquire a nuclear weapon."

President Obama stressed the shared responsibility of all nations in securing the world's most dangerous weapons. "If we fail to stand together, then. . . . international law will give way to the law of the jungle. And that benefits no one."