Taking an assertive tone against Iran without dictating a specific deadline for action, Mr. Obama warned that the United States would eventually look past diplomacy for a way to contain Iran's nuclear ambitions.

"America wants to resolve this issue through diplomacy, and we believe that there is still time and space to do so. But that time is not unlimited," Mr. Obama said. "We respect the right of nations to access peaceful nuclear power, but... the United States will do what we must to prevent Iran from obtaining a nuclear weapon."

On Monday, Iranian President Mahmoud Ahmadinejad maintained his country's project to enrich uranium is only for peaceful purposes. Ahmadinejad expressed optimism that Iran could reach a diplomatic resolution with the U.S., but he also berated the U.S. for defending Israel, referring to Israel as a nuclear-armed "fake regime."

Mr. Obama on Tuesday also took the Assad regime in Syria to task, charging, "In Syria, the future must not belong to a dictator who massacres his people."

He said the U.S. will work for "sanctions and consequences for those who persecute; and assistance and support for those who work for this common good. Because we believe that the Syrians who embrace this vision will have the strength and legitimacy to lead."

Mr. Obama called on all world leaders to reject political violence and extremist views.

"The impulse towards intolerance and violence may initially be focused on the West, but over time it cannot be contained," he warned. "The same impulses toward extremism are used to justify war between Sunnis and Shia, between tribes and clans. It leads not to strength and prosperity but to chaos."

He specifically decried the violence across the Muslim world sparked by an American-produced, anti-Islam video. The president clarified that he considered it a "crude and disgusting" video and that it had nothing to do with the views of the U.S. government but noted that "Americans have fought and died around the globe" to protect free speech.

"I know that not all countries in this body share this understanding of the protection of free speech," Mr. Obama continued. "Yet in 2012, at a time when anyone with a cell phone can spread offensive views around the world with the click of a button, the notion that we can control the flow of information is obsolete. The question, then, is how we respond. And on this we must agree: there is no speech that justifies mindless violence."