Obama highlighted battles in which U.S.-aligned fighters have prevailed against the group, including combat in the Syrian cities of Kobane and Tal Abyad and the Iraqi city of Tikrit. He said Islamic State fighters have lost more of than a quarter of the populated territory they had captured in Iraq.

But the group continues to control some of Iraq's most important cities and holds sway in unpopulated areas that are more difficult for government forces to control. In May, Iraqi forces ceded the city of Ramadi to Islamic State when they retreated en masse.

U.S. military personnel in Iraq have struggled to ensure that Iraqi forces - which remain reliant on Shiite paramilitary fighters and lack capability in key areas such as logistics, intelligence and air power - can effectively take on Islamic State.

"As with any military effort, there will be periods of progress, but there are also going to be some setbacks," Obama said.

Obama, who has sought to limit American involvement in overseas conflicts, said the battle would ultimately be fought by local forces, not Americans. Since last summer, Obama has sent about 3500 U.S. advisers and trainers back to Iraq, but he has also vowed to keep American troops out of combat there.

After his discussions with defense leaders on Monday, the President said he had no immediate plans to send additional troops to Iraq.

He said the United States was now "speeding up" the training of Iraqi forces. "This aspect of our strategy was moving too slowly, but the fall of Ramadi has galvanized the Iraqi government," he said.

American officials are also grappling with the widespread appeal of the extremist group, an al-Qaeda offshoot that has recruited fighters from around the world and has inspired attacks across the Middle East, in Europe and beyond. Most of those attacks have targeted Westerners or Shiite Muslims, whom Islamic State considers infidels.