"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 US state of Maryland, Xinhua reported.

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

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 US-led bombing campaign.

IS militants 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," he said.

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