President Barack Obama issued a challenge to world leaders and had strong words for Iran and its nuclear aspirations while addressing the United Nations General Assembly Tuesday.

The president began his speech by paying tribute to Ambassador Chris Stevens, who was recently killed at the U.S. consulate in Libya.

He also condemned the anti-Islamic film that has triggered violent protests throughout the Middle East, calling it an insult to all Americans and challenged world leaders to confront the root causes of rage in the Muslim world.

"I do believe that it is the obligation of all leaders, in all countries, to speak out forcefully against violence and extremism," said Obama. "It is time to marginalize those who - even when not resorting to violence - use hatred of America, or the West, or Israel as a central principle of politics. For that only gives cover, and sometimes makes excuses, for those who resort to violence."

The president also spoke at length about Iran, saying he believes the dispute over Iran's nuclear program can be resolved through diplomacy but accused the country of failing to demonstrate their nuclear program is peaceful and said Iran has failed to meet its obligations to the UN.

Iranian President Mahmoud Ahmadinejad is scheduled to address the General Assembly Wednesday.

Early this afternoon, Obama also delivered a speech at the Clinton Global Initiative in Midtown, focusing on his administration's efforts to fight sex trafficking.

"As president, I've made it clear that the United States will continue to be a leader in this global movement. We've got a comprehensive strategy and we're shining a spotlight on the dark corners, where it persists," said the president.

Obama also urged his audience to only buy products that are made "free of forced labor."

The president's travel means rolling street closures and gridlock on the East Side of Manhattan.

Streets that remain closed to traffic for the duration of the UN General Assembly include First Avenue from 42nd Street to 48th Street, and 44th, 45th and 46th Streets from First to Second Avenue.

Additionally, 42nd Street from the FDR Drive to Second Avenue, and the 42nd Street exit and entrance ramps of the Drive will be closed from 5 a.m. until the end of each day's session.

Earlier Tuesday, Republican presidential candidate Mitt Romney also spoke at the Clinton Global Initiative, despite the fact that Clinton has campaigned heavily for Obama.

During his remarks, the former Massachusetts governor touted the benefits of promoting and maintaining a free market.

"Free enterprise as we know has done more to bless humanity than any other economic system," said Romney. "Not only because it’s the only system that creates a prosperous middle class, but also because it’s the only system where the individual enjoys the freedom to guide and build his or her life."

Romney noted the U.S. provides the most foreign aide than any other nation in the world, but that it should not be used to sustain a developing country on a permanent basis.

Instead, he says, U.S. foreign policy should emphasize the rewards of self-reliance.

Romney also touched on the recent killing of U.S. Ambassador Chris Stevens, saying the U.S. must play a role in stabilizing areas like Benghazi while holding those responsible for violent attacks accountable.

On Monday, Romney criticized President Obama for comments he made during an interview on CBS' "60 Minutes".

Romney accused the president of minimizing the attack as a bump in the road.

The White House called Romney's accusations "desperate and offensive."