The United Nations Security Council in a rare meeting of heads of state, led for the first time by a US president, adopted a resolution on Thursday focused on stopping the spread of nuclear weapons.
With President Obama acting as chairman, the council unanimously passed the resolution aimed at ensuring full compliance with international arms agreements from countries like North Korea and Iran, which have either banned inspectors or severely limited their access.
Obama said, though, that the resolution was not about singling out nations, but about ensuring that international agreements have real-world heft.
"International law is not an empty promise, and treaties must be enforced," Obama said.
President Obama challenged the gathering to overcome cynicism against the goal of ridding the world of nuclear arms. He quoted president Reagan, saying "a nuclear war can never be won and must never be fought."
"The world must stand together," Obama said. "We must demonstrate that international law is not an empty promise."
It was the first Security Council summit chaired by a US president, and only the fifth time that Security Council heads of state have met. Obama led the meeting because the United States holds the revolving presidency of the Security Council in September.
Both Obama and Russian President Dimitry Medvedev, who spoke later, noted that the world's two nuclear superpowers were working on reducing their stockpiles in advance of a global nuclear summit scheduled for next year.
"It's obvious that an effective solution ... depends on the constructive engagement of all parties," Medvedev said, adding that he expected the Russia-US leadership on the issue to be backed by "all nuclear powers".
On Wednesday, Medvedev signalled he could support sanctions against Iran over its efforts to develop a nuclear weapon.
"Russia's position is clear: sanctions rarely lead to productive results, but in some cases sanctions are inevitable," Medvedev said in a joint appearance with Obama after they met in New York.
The statement bolsters US-led efforts for increased international pressure on Iran to adhere to non-proliferation agreements in pursuing the development of nuclear energy.
Iran claims its nuclear programme is intended for peaceful purposes, but the international community accuses it of continuing to try to develop nuclear weapons capability.