President Obama on Monday acknowledged slow progress in the fight against Islamic State militants in the Middle East but signaled he has no immediate plans to send more U.S. troops into Iraq, saying that won't fix the region's long-term problems.

"This will not be quick. This is a long-term campaign," the commander in chief warned. "ISIL is opportunisitic and nimble. … It will take time to root them out, and doing so must be the job of local forces on the ground, with training and air support from our coalition."

Obama's comments came during a rare Pentagon visit following a meeting with 35 members of his national security team and other key administration advisers to determine "what's working and what we can do better" in the region, a military campaign that hits its one-year anniversary next month.

The president noted that over the last 11 months, more than 5,000 airstrikes have been launched against ISIL fighters and positions, resulting in the militant group losing "more than a quarter" of the populated area it had claimed in Iraq.

But Obama also acknowledged the obvious: the campaign against ISIL is slow moving.

There are 3,550 U.S. personnel on the ground in Iraq. Obama said those forces and airstrikes can do only so much to address the "political and economic" realities that allowed the militants to grow in popularity and strength in the region.

Obama did not flatly rule out a future U.S. troop increase in Iraq — something that top Pentagon leadership has hinted is on the table — but said military advisers have repeatedly warned that foreign fighters alone cannot defeat the enemy.

"In order for us to succeed long-term in this fight against ISIL, we have to develop local security forces that can sustain progress," he said. "It is not enough to send in American troops to temporarily set back terrorist groups like ISIL, but to then, once we leave, see that void filled with extremists."

Defense Secretary Ash Carter and Joint Chiefs Chairman Gen. Martin Dempsey will defend that strategy on Capitol Hill on Tuesday in a hearing before the Senate Armed Services Committee.

Obama's strategy in the region has come under intense criticism in recent weeks from conservatives in Congress, in light of new Islamic State advances in Iraq.

Obama preached patience on those setbacks, reaffirming confidence in the U.S. troops and noting that recent outreach efforts have boosted the number of Iraqi recruits to fight the advancing enemy.

"The fall of Ramadi has galvanized the Iraqi government," he said, referring to the key Iraqi city that is under Islamic State control.

He also suggested that impatient members of Congress should move ahead on the confirmation of a new Treasury undersecretary, to help with the fight against the illicit financial operations of the militant group.

Those comments are unlikely to sway skeptical lawmakers. In a statement released before Obama's remarks, House Armed Services Committee Chairman Rep. Mac Thornberry, R-Texas, said it's clear that the president's "strategy to defeat ISIL isn't working" and needs dramatic changes.

"From Libya and Tunisia, to Afghanistan, ISIL continues to advance while we lose ground and time," Thornberry said. "I hope that the president will acknowledge these realities, end the veto threats on bills that would enhance his ability to take the fight to ISIL, and rethink his own inadequate strategy."

Obama also has taken criticism over a possible veto threat to the annual defense authorization bill on issues of federal spending caps and use of the overseas war funds.

When pressed on Monday, Obama sidestepped the question directly, but insisted that troops will be paid.

"You'll note I've now been president for six and a half years, and we've had some wrangling with Congress in the past. Our service members haven't missed a paycheck," he said.

"What we're not going to do is accept a budget which shortchanges our long term requirements for new technologies, for readiness."