Obama hosted a UN gathering of world leaders working to expand the battle against terrorism, a day after he and the leaders of Russia, China and Iran addressed the General Assembly during its 70th anniversary.
Although the war on terrorism, particularly in Syria, has caught the attention of top leaders around the world, there has been no overall agreement on how to end the conflict.
Obama committed military, intelligence and economic means to defeat the Islamic State, but acknowledged that the resilient group has established roots in Syria and Iraq and continues to expand.
"I have repeatedly said that our approach will take time. This is not an easy task," he cautioned, while adding that he was "ultimately optimistic" the brutal organization would be defeated because it has nothing to offer but suffering and death, Reuters reported.
Obama's strategy is at odds with that of Russia, which has offered support in the fight against Islamic State, but backs Syrian President Bashar al-Assad. Washington insists that al-Assad must be removed from power.
One option that reportedly will not be available in the fight against Islamic State is the United States' $500 million program aimed at training and equipping moderate Syrian rebels.
The Pentagon reportedly is suspending the program, which only sent two classes of fighters to Syria. The first class of 54 fighters was overrun quickly, while the second almost immediately surrendered its weapons and vehicles to al-Qaeda.
Also on Tuesday, UN Secretary-General Ban Ki-moon said the UN's most recent data shows a 70% increase in foreign terrorist fighters from more than 100 countries to regions in conflict, Reuters reported.
According to a House of Representatives Homeland Security Committee study released Tuesday, the United States is doing too little to stop the flow of fighters to the Islamic State.
Nearly 30,000 foreigners, including more than 250 Americans, have joined Islamic State and other militant groups to fight in Syria and Iraq, double the number a year ago, the report said.
Several dozen of the fighters have made their way back to the United States, the report said. Additionally, 5,000 of the 30,000 carry western passports that would allow them to enter the United States without visas, according to the report.
"The stats are alarming. Nearly 70 [Islamic State]followers have been arrested in the last year in the United States of America," Republican Representative Michael McCaul, the committee's chairman, told a news conference.
