President Barack Obama warned that "dangerous currents" threaten to create a "darker world" in a wide-ranging address to the United Nations General Assembly on Monday.
Obama slammed Syrian leader Bashar al-Assad as a "tyrant" and urged the international community to work together to defeat ISIS.
"There is no room for accommodating an apocalyptic cult like ISIL," the president said, using an alternative name for the terrorist group.
The president also stressed that the United States " is prepared to work with any nation, including Russia and Iran, to resolve the conflict" in Syria.
"We must recognize that there cannot be, after so much bloodshed, so much carnage, a return to the prewar status quo," the president said.
President Obama also addressed issues including the Iran nuclear accord, the bloodshed in Syria, the rise of ISIS, Cuba relations and tensions with Russia. Obama pointed to the nuclear deal — a historic accord between Tehran and six world powers aimed at curbing Iran's nuclear program — as an example of what can be accomplished by international cooperation when nations are held accountable for violating international rules, and principled diplomacy is pursued to achieve our objectives.
"For two years, the United States and our partners including Russia, including China…stuck together," President Obama said adding that the deal's hoped for success would ultimately make the world safer. "That is the strength of the international system when it works the way it should."
Obama highlighted the normalization of relations between the U.S. and Cuba and stressed that the embargo against that country should be lifted. He added that "Cuba will find its success if it pursues cooperation with other nations."
Obama also underscored the need for countries to work together to battle the Islamic State.
The president also took pointed aim at Russia.
Relations between the two nations have plummeted to Cold War-level lows amid tension over Russia's annexation of portions of Ukraine and growing Russian military presence near the Syrian port city of Latakia. During the morning's events, Secretary of State John Kerry crossed the General Assembly floor to hug Ukrainian President Petro Poroshenko.
The U.S. and Russia diverge on Assad's leadership. Obama focused on the need for a political transition in Syria stressing that Assad must relinquish power, while Putin put Assad up as the only option to defeat ISIS.
"By this logic," the president said, countering Russia's position "We should support tyrants like Bashar al Assad…because the alternative is surely worse."
"When a dictator slaughters tens of thousands of his own people it's not a matter of one nation's internal affairs," Obama said.
The U.S. supports rebels fighting Assad, but both Washington and Moscow have a common enemy in ISIS — the target of U.S.-led airstrikes.
Obama also chastised Russia for its actions in annexing portions of Ukraine and said the U.S. continues to press for the crisis to be resolved.
"If that happens without consequence in Ukraine it could happen to any nation represented here today," Obama said adding later, "Imagine instead if Russia had engaged in true diplomacy."
Later on Monday, Putin told the General Assembly that supporting Assad was the only way to curtail ISIS and stem the overwhelming flow of refugees.
"It would be a mistake not to cooperate with the Syrian government," Putin said.
The Russian leader made the same point in his interview with "60 Minutes," saying that "there is no other solution to the Syrian crisis than strengthening the effective government structures and rendering them help in fighting terrorism."
Attention at the gathering will be focused on the first meeting between President Obama and Russian President Vladimir Putin in nearly a year.
The president on Monday is also expected to co-host a summit on international peacekeeping with eight other nations and U.N. Secretary-General Ban Ki-moon.
Ahead of Obama's address, the White House stressed that U.N. peacekeeping has never been "more stretched or more important than it is to international peace and security right now."
Obama's address comes on the heels of a speech on Sunday in which he made the case for world leaders to work together on eliminating global hunger and poverty by supporting a 15-year development agenda that will require trillions of dollars of effort from countries, companies and civil society. In a possible nod toward his address today, he noted that "military interventions might have been avoided over the years" if countries had spent more time, money and effort on caring for their own people.
"Development is threatened by war," Obama said, and war often arises from bad governance. Addressing the world's greatest refugee crisis since World War II as millions flee conflict in Syria and elsewhere, the U.S. president said countries "that can, must do more to accommodate refugees" but added those efforts "must be matched by hard work of diplomacy."