"There has to be a strong international outrage at what's taking place," Mr. Obama said in a press conference in L'Aquila, Italy, where the G8 summit has wrapped up. He called striking a balance between meeting that moral obligation and respecting national sovereignty "one of the most difficult questions in international affairs."
"I don't think there is a clean formula," he said. "In general, it is important for the sovereignty of nations to be respected."
Mr. Obama added that conflicts should be resolved through diplomacy and setting up international norms that countries want to meet.
The question of respecting national sovereignty versus protecting international human rights lingered at the end of the G8 summit as new protests against the outcome of the Iranian presidential election cropped up yesterday in Tehran.
The Group of Eight countries released a statement on Wednesday which says the participating nations "deplore" the post-election violence, and consider interference with media, unjustified detentions of journalists and recent arrests of foreign nationals in Iran "unacceptable."
Mr. Obama defended the toothless statement, saying, "This notion that we were trying to get sanctions (at the G8 summit), or that this was a forum in which we could get sanctions was not accurate."
"I think the real story here was consensus in that statement, including (from) Russia, which doesn't make statements like that lightly," he said.
There are always going to be objections to international interventions, Mr. Obama said, but "there are going to be exceptional circumstances in which the need for international intervention becomes a moral imperative."
He said the most obvious example was the genocide that occurred in Rwanda.
Mr. Obama told of an anecdote that British Prime Minister Gordon Brown shared during the summit meetings, about a trip he made to a museum in Rwanda marking the genocide. There was a picture of a 12-year-old boy in the museum and a biography of the child next to the picture.
"The last line on this exhibit said that right before he and his mother were killed, he turned to his mother and said, 'Don't worry, the United Nations is going to come save us,'" related Mr. Obama.
"That voice has to be heard in international relations," he said.
Mr. Obama said his administration aims to address conflicts on the international stage on a case-by-case basis.
"Rather than focus on hypotheticals, what my administration wants to do is build up international norms, put pressure on governments," he said, "not hypothesize on particular circumstances."
Along with providing a unified statement against the violence in Iran, Mr. Obama said it was noteworthy that the G8 nations agreed to re-evaluate Iran's posture towards negotiating the cessation of its nuclear weapons policy at the G20 meeting in September.
"The international community has said, 'Here's a door you can walk through,'" he said. "That's been our premise -- that we provide that door, but we also say we're not going to wait indefinitely and wait for the development of a nuclear weapon, the breach of international treaties and wake up one day and find ourselves in a much worse situation."
More on the press conference: