"I think this shows that, when we can work together toward a common purpose, that the United States can be as multilateral as anyone," he said in an interview with National Public Radio (NPR) aired Thursday.
"We have worked within the international community, with the International Atomic Energy Agency. We have worked with our European Union friends, and especially, as they're called, the EU 3 -- France, Germany and the United Kingdom -- to come up with a good resolution," Powell told NPR.
He stressed that "it was the United States who kept telling our European Union friends and our Russian friends and other friends around the world: Iran is developing nuclear weapons."
"We kept insisting that we had good information, and everybody thought that the United States was just playing that 'axis of evil' card," Powell said, referring to the moniker given by President George W. Bush to Iran, Iraq and North Korea.
"Well, guess what? Finally, the world saw the evidence," he said.
"And the International Atomic Energy Agency (IAEA), under Dr. (Mohamed) ElBaradei, showed that Iran has been failing in its obligations to the Nonproliferation Treaty and the other obligations they have, and they have been working on programs that could lead to the development of a nuclear weapon, and now they have been called to account."
The UN nuclear watchdog unanimously condemned Iran Wednesday for nearly two decades of covert nuclear activities but did not recommend that Tehran face possible UN sanctions.
Iran hailed the resolution adopted by the IAEA as a diplomatic victory, saying it showed that Tehran had been honest about its nuclear program despite "the uproar from certain oppressive circles," a reference to the US push for a tougher response.
ElBaradei said the resolution by the agency's board of governors was meant as "a very serious and ominous message" for Iran to comply with the nuclear nonproliferation treaty, which seeks to prevent the spread of nuclear weapons.
The resolution, drawn from a report prepared by ElBaradei, said Iran had failed "over an extended period of time" to meet obligations on "the reporting of nuclear material and its processing and use," including separating plutonium and enriching uranium.