The UN Security Council unanimously approved a resolution aimed at ridding the world of nuclear weapons today.
Russia, China and developing nations supported the US-sponsored measure, giving it global clout and strong political backing.
The resolution calls for stepped up efforts to prevent the spread of nuclear weapons, promote disarmament and "reduce the risk of nuclear terrorism."
It was only the fifth time the Security Council met at summit level since the UN was founded in 1945. And Barack Obama was the first American president to preside over a Security Council summit.
"The historic resolution we just adopted enshrines our shared commitment to a goal of a world without nuclear weapons," Mr Obama said immediately after the vote. "And it brings Security Council agreement on a broad framework for action to reduce nuclear dangers as we work toward that goal."
Just one nuclear weapon set off in a major city could cause major destruction, Mr Obama said.
He said the global effort would seek to "lock down all vulnerable nuclear materials within four years."
"This is not about singling out an individual nation," he said. "International law is not an empty promise, and treaties must be enforced."
"We will leave this meeting with renewed determination," Mr Obama said.
UN Secretary-General Ban Ki-moon saluted the national leaders for joining in the unprecedented Security Council summit on nuclear arms.
"This is a historic moment, a moment offering a fresh start toward a new future," he said.
Russian President Dmitry Medvedev said that "our main shared goal is to untie the problem knots" among nations seeking nuclear non-proliferation and disarmament.
"This is complicated since the level of mistrust among nations remains too high, but it must be done," he said.
Mr Obama aides see adoption of the resolution as an endorsement of the president's entire nuclear agenda, as laid out in his April speech in Prague. He declared his commitment to "a world without nuclear weapons."
The president called in that speech for the slashing of U.S. and Russian nuclear arsenals, adoption of the treaty banning all nuclear tests, an international fuel bank to better safeguard nuclear material, and negotiations on a new treaty that "verifiably" ends the production of fissile materials for atomic weapons.
He also strongly backed the Nuclear Non-proliferation Treaty, or NPT, which requires signatory nations not to pursue nuclear weapons in exchange for a commitment by the five nuclear powers to move toward nuclear disarmament. States without nuclear weapons are guaranteed access to peaceful nuclear technology for electricity generation.
All those measures are included in the draft resolution.
In its opening paragraph, the draft reaffirms the council's commitment "to seek a safer world for all and to create the conditions for a world without nuclear weapons."
Arms control advocates say those elements are interconnected. Some nations might eventually reject the limitations of the Non-proliferation Treaty, for example, if the U.S. and other nuclear powers don't abide by that treaty's requirement to move toward disarmament by reducing their arsenals, or if they reject the test ban.
The draft resolution does not mention any country by name but it reaffirms previous Security Council resolutions that imposed sanctions on Iran and North Korea for their nuclear activities. It does not call for any new sanctions.
The draft "expresses particular concern at the current major challenges to the non-proliferation regime that the Security Council has acted upon."
It also calls on all countries that are not parties to join the treaty "to achieve its universality at an early date," and in the interim to comply with its terms. The major countries that are not members of the NPT are India and Pakistan, which have conducted nuclear tests, and Israel which is believed to have a nuclear arsenal.