WASHINGTON, Oct. 14 -- U.S. President Barack Obama on Tuesday warned that there would be periodic "setbacks" in the fight against the Islamic State (IS), saying it is "a long-term campaign."

"This is going to be a long-term campaign; there are no quick fixes involved," Obama said after a meeting with coalition military leaders at Joint Base Andrews in the U.S. state of Maryland.

There are "going to be periods of progress and setbacks," he added.

The president acknowledged that the terror network, which controls large swaths of land in Iraq and Syria, does not present a "classic" military challenge.

"What we're also fighting is ideological," Obama said, appealing that the United States and the rest of the 60 nations participating in the effort against IS be "united in our goal."

The meeting with international military leaders, top White House officials, and top Pentagon brass was held amid new fears that IS is still making gains in both Iraq and Syria despite a U.S.-led bombing campaign.

IS forces have reportedly captured a military training camp in western Iraq and lobbed bombs at Baghdad suburbs, sparking concerns that the Iraqi military is not up to the fight.

But the White House maintained that despite some of the troubling news, the president's plan against IS was "succeeding."

"We're in the early days of the execution of that strategy," said press secretary Josh Earnest during a White House press briefing on Tuesday. "But certainly the early evidence indicates that this strategy is succeeding."

Earnest pointed out that U.S. humanitarian missions successfully protected Iraqi minorities under siege from IS, and had also driven the group from a pair of crucial dams.

But he also conceded that without ground forces, the United States would not be able to prevent all IS advances.

"I don't think anybody has sought to leave you or anyone else with the impression that these kinds of airstrikes were going to dramatically reverse the situation on the battlefield overnight. They won't. We've been pretty candid about the fact that this is a longer-term proposition," Earnest said.