Addressing the U.N. General Assembly in New York, he highlighted efforts to build an international coalition to combat the group that has taken over large areas in Syria and Iraq.
“This group has terrorized all who they come across in Iraq and Syria," he said. "Mothers, sisters and daughters have been subjected to rape as a weapon of war. Innocent children have been gunned down. Bodies have been dumped in mass graves. Religious minorities have been starved to death. In the most horrific crimes imaginable, innocent human beings have been beheaded, with videos of the atrocity distributed to shock the conscience of the world.
“In this effort, we do not act alone. Nor do we intend to send U.S. troops to occupy foreign lands," he added, saying that more than 40 nations have offered to join U.S.-led efforts to conduct airstrikes against militant strongholds in Syria and Iraq.
"We will train and equip forces fighting against these terrorists on the ground," he said. "We will work to cut off their financing, and to stop the flow of fighters into and out of the region."
Laying out a broad vision of American leadership in a changing world, the president also emphasized U.S. efforts in areas where he see increasing momentum among allies: containing Ebola; holding forth with sanctions on Russia while supporting efforts to maintain a ceasefire in Ukraine, and executing a broad international vision for combating climate change.
"Each of these problems demands urgent attention," he said. "But they are also symptoms of a broader problem — the failure of our international system to keep pace with an interconnected world.
"We have not invested adequately in the public health capacity of developing countries," he said. "Too often, we have failed to enforce international norms when it’s inconvenient to do so. And we have not confronted forcefully enough the intolerance, sectarianism, and hopelessness that feeds violent extremism in too many parts of the globe."
Obama had tough words for Russia.
“Russia’s actions in Ukraine challenge this post-war order,” he said, citing the country's February annexation of Crimea followed by the arrival of Russian arms in Eastern Ukraine, where a violent separatist conflict has killed thousands.
"When a civilian airliner was shot down from areas that these proxies controlled, [pro-Russian separatists] refused to allow access to the crash for days," he said. "When Ukraine started to reassert control over its territory, Russia gave up the pretense of merely supporting the separatists, and moved troops across the border.
“This is a vision of the world in which might makes right — a world in which one nation’s borders can be redrawn by another, and civilized people are not allowed to recover the remains of their loved ones because of the truth that might be revealed,” he said, vowing to U.S. support for Kyiv and reinforcements for NATO allies. “America stands for something different. We believe that right makes might — that bigger nations should not be able to bully smaller ones; that people should be able to choose their own future.
The president also called for concrete steps to fight Ebola in West Africa during his speech.
"As we speak, America is deploying our doctors and scientists — supported by our military — to help contain the outbreak of Ebola and pursue new treatments," Obama said. "But we need a broader effort to stop a disease that could kill hundreds of thousands, inflict horrific suffering, destabilize economies, and move rapidly across borders."
The president said the U.S. would continue to mobilize other countries to assist in the effort to curb the outbreak and "enhance global health security in the long-term."
His comments come on the heels of a new U.S. Centers for Disease Control and Prevention (CDC) report Tuesday that between 550,000 and 1.4 million people in West Africa could be infected with the Ebola virus by January 20, 2015.
Based on the assumption that the actual number of Ebola cases has been underreported, the CDC said in a statement that "extensive, immediate actions — such as those already started — can bring the epidemic to a tipping point to start a rapid decline in cases."
The agency's best-case model projects that by getting 70 percent of patients into facilities where the risk for transmission is reduced and burying the dead safely, the epidemic would be "almost ended" by January 20.
Iranian diplomacy; 'Asia pivot'; Gaza
On Iran, the president said his administration is committed to diplomacy.
“America is pursuing a diplomatic resolution to the Iranian nuclear issue, as part of our commitment to stop the spread of nuclear weapons and pursue the peace and security of a world without them. This can only happen if Iran takes this historic opportunity,” he said. “My message to Iran’s leaders and people is simple: do not let this opportunity pass. We can reach a solution that meets your energy needs while assuring the world that your program is peaceful.”
President Obama said too that his “Asia pivot” engagement remains.
“America is and will continue to be a Pacific power, promoting peace, stability, and the free flow of commerce among nations. But we will insist that all nations abide by the rules of the road, and resolve their territorial disputes peacefully, consistent with international law,” he said. “That’s how the Asia-Pacific has grown. And that’s the only way to protect this progress going forward.”
As for the fight against global poverty, President Obama said the U.S. intends to maintain a key role.
"America is committed to a development agenda that eradicates extreme poverty by 2030. We will do our part — to help people feed themselves; power their economies; and care for their sick," he said. "If the world acts together, we can make sure that all of our children can enjoy lives of opportunity and dignity."
The president also touched on the Arab-Israeli peace process, saying "As bleak as the landscape appears, America will never give up the pursuit of peace.
"The violence engulfing the region today has made too many Israelis ready to abandon the hard work of peace. But let’s be clear: the status quo in the West Bank and Gaza is not sustainable," he said. "We cannot afford to turn away from this effort — not when rockets are fired at innocent Israelis, or the lives of so many Palestinian children are taken from us in Gaza.
"So long as I am President, we will stand up for the principle that Israelis, Palestinians, the region, and the world will be more just with two states living side by side, in peace and security."
Targeting extremist recruitment
Later Wednesday, Obama will chair a U.N. Security Council meeting where members are expected to adopt a resolution addressing the flow of foreign fighters traveling to join terror groups.
The meetings follow the U.S. military's expansion of its air campaign against the Islamic State group from areas in Iraq to airstrikes targeting the militants in Syria.
In opening remarks at the U.N. General Assembly Wednesday, Secretary-General Ban Ki-moon said human rights are under fire around the world.
"From barrel bombs to beheadings, from the deliberate starvation of civilians to the assault on hospitals, UN shelters and aid convoys, human rights and the rule of law are under attack," Ban said. "We need decisive action to stop atrocity crimes and frank discussions on what created the threat in the first place," the U.N. chief said, citing the "new depths of barbarity" in Syria and Iraq by jihadists.
The London-based Syrian Observatory for Human Rights reported new airstrikes overnight in northern Syria, along an area near Turkey where a militant advance last week sent 130,000 people fleeing across the border.
Syrian forces have conducted their own airstrikes against militants and opposition fighters throughout the country's three-year civil war.
The United States said Tuesday it launched the attacks against the Islamic State in Syria because the Syrian government cannot and will not stop the militants from setting up safe havens.
U.S. Ambassador to the U.N. Samantha Power wrote in a letter to U.N. Secretary-General Ban Ki-moon that the Islamic State group had used safe havens inside Syria to train, finance and launch attacks against the Iraqi people.
She wrote that the U.N. Charter calls on member states to prevent such actions on its territory. She said Syria is unwilling or unable to do that.
President Obama said the U.S. will not tolerate safe havens for terrorists who threaten Americans.
State Department spokeswoman Jen Psaki said the U.S. did not request permission from Syrian President Bashar al-Assad for the airstrikes, but had notified the country's U.N. representative that action would be taken.