"The United States of America will work with a broad coalition to dismantle this network of death," Obama told the UN General Assembly. "Today I ask the world to join in this effort."
US President also denounced the Russian aggression in Europe on Wednesday, but said Washington would lift sanctions if Moscow changes course.
"Russian aggression in Europe recalls the days when large nations trampled small ones in pursuit of territorial ambition," Obama said, adding that a recent ceasefire agreement in Ukraine offers an opening towards diplomacy and peace.
"If Russia takes that path - a path that for stretches of the post-Cold War period resulted in prosperity for the Russian people - then we will lift our sanctions and welcome Russia's role in addressing common challenges."
He also urged Iran to seize the "historic opportunity" of reaching a deal with world powers on its contested nuclear program.
"My message to Iran's leaders and people is simple: do not let this opportunity pass," said Obama.
During his speech at the UN, Obama acknowledged that the United States had its own racial and ethnic tensions.
"Yes, we have our own racial and ethnic tensions. And like every country, we continually wrestle with how to reconcile the vast changes wrought by globalization and greater diversity with the traditions that we hold dear," he said.
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