The president would not rule out military options. But he says his preferred course of action is to resolve the standoff diplomatically. (See Obama on Iran and G-20 at left.)
Earlier, Obama and the leaders of France and Britain accused the Islamic republic of clandestinely building an underground plant to make nuclear fuel. Obama called the international response "an unprecedented show of unity."
Obama also asserted that he and other leaders of the world's 20 largest economies took actions that "brought the global economy back from the brink" and saved or created millions of jobs.
"We leave here today confident and united," he said at the conclusion of a two-day summit to deal with the worst economic crisis since the 1930s.
He spoke as world leaders lined up behind sweeping promises designed to fix a malfunctioning global economic system in hopes of heading off future financial meltdowns.
The leaders agreed to leave stimulus programs in place for now until recoveries are more firm. "We must make sure that when growth returns, jobs do, too," he told a wrap-up news conference.
"We brought the global economy back from the brink. We laid the groundwork today for long term prosperity," Obama said.
"It is important to recall the situation we faced" in April when the Group of 20 leaders last met and when talk was rampant about a second Great Depression.