In his opening statement testifying before the House Armed Services Committee, Defense Secretary Chuck Hagel said U.S. forces had made progress against Islamic State fighters but that the militants were adapting and that pressure on them should be sustained. (AP)

U.S. military leaders defended the Obama administration’s strategy against the Islamic State on Thursday, arguing before skeptical lawmakers that President Obama’s plan to put Iraqi forces at the forefront of the fight had achieved some limited battlefield success while laying the groundwork for a larger, long-term campaign against the group.

Defense Secretary Chuck Hagel told members of the House Armed Services Committee that months of U.S. and allied airstrikes and growing on-the-ground support for Iraq’s military had stalled or reversed the Islamist group’s advance in certain areas of Iraq.

“Sustaining this pressure on ISIL will help provide time and space . . . for Iraq to reconstitute its forces and continue going on the offense,” Hagel said, using another name for the extremist group that now controls a vast expanse across Iraq and Syria.

Among the tactical successes that Hagel described was Iraqi Kurdish forces’ expulsion of Islamic State militants from the northern town of Zumar and Iraqi forces’ advance into areas around the Baiji oil refinery after weeks of fighting.

But in a reminder of the Iraqi government’s tenuous position five months after militants streamed into northern Iraq, a suicide bombing killed a group of soldiers on Tuesday in an area of Baiji nominally under government control.

A protester brandishing a sign that read, "There is no military solution" was escorted out after interrupting a hearing where Defense Secretary Chuck Hagel and Chairman of the Joint Chiefs of Staff Gen. Martin Dempsey were testifying about the fight against the Islamic state on Thursday. (AP)

Thursday’s hearing gave Hagel and Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, an opportunity to press Congress to approve funding for Obama’s plan to roughly double the U.S. force in Iraq, which is now about 1,400 service members.

The White House is asking Congress to provide $5.6 billion for its operation against the Islamic State, in part to set up a program to retrain 12 Iraqi brigades and to expand the U.S. mission to advise Iraqi military commanders.

Hagel and Dempsey faced questions from lawmakers apprehensive about numerous aspects of the administration’s strategy for Iraq and for neighboring Syria, now in the fourth year of a civil war that has killed almost 200,000 people.

“My fundamental question is how can you successfully execute the mission you’ve been given to degrade and ultimately destroy ISIL when some of your best options are taken off the table,” said Howard P. “Buck” McKeon, the Republican committee chair.

Obama, who ended the United States’ last war in Iraq in 2011, has pledged that U.S. forces will not return to ground combat there.

U.S. officials have acknowledged that the limited battlefield advances by Iraqi forces to date have not altered the strategic picture across Iraq. While Iraqi troops, peshmerga forces and Shiite militiamen are making sporadic progress, they are unlikely to attempt to recapture the strategic northern city of Mosul until well into next year.

Dempsey suggested that U.S. forces, now limited to training and advising Iraqi troops, might get closer to the front lines when a decision is made to go after Mosul. But he played down the possibility of a major U.S. buildup.

Kurdish fighters battle to push Islamist militants out of Kobane, as the United Nations says Islamic State commanders are liable for mass war crimes. (Reuters)

“One of our assumptions is that the government of Iraq will be inclusive. One of the assumptions is that the Iraqi security forces will be willing to take back al-Anbar province and Nineveh province,” where Mosul is located, Dempsey said. “If those assumptions are rendered invalid, I will have to adjust my recommendations.”

Other legislators questioned the need for any renewed operations in Iraq.

“This is especially important given the lessons of the last decade when, despite seven years of conflict in Iraq, 4,500 American lives lost, and more than $1.5 trillion spent, our military effort did not resolve the sectarian conflict we are now confronted with,” said Niki Tsongas (D-Mass.).

Hagel said there was reason to believe Iraq’s army, which partly collapsed in the face of the Islamic State’s advances, may perform better with renewed U.S. attention.

This week, Iraqi Prime Minister Haider al-Abadi replaced dozens of his military commanders. He has also installed a defense minister from Iraq’s Sunni Muslim minority, whose support is seen as crucial to turning the tide against the Sunni Islamic State.

U.S. officials are planning to resume a training mission that was a focal point of the 2003-2011 war in Iraq and cost more than $20 billion. Dempsey said three well-trained divisions, or about 80,000 troops, would be required to reclaim Mosul.

“Overall, I’m wondering how we can be walking down this same path that we walked down over the last decade or more and hope for a different outcome,” said Tulsi Gabbard (D-Hawaii), an Iraq veteran.

Hagel and Dempsey were asked what the United States could hope to accomplish without directly attacking Syrian President Bashar al-Assad, whose actions helped to fuel the Islamic State’s expansion.

They described a long-term effort to establish a more stable government in Syria, in part through a program to train moderate Syrian rebels who over time might combat Assad.

“But ISIL is right now, and ISIL is threatening the country of Iraq,” Hagel said. “And so that’s why we are dealing with that component first, because we must.”

Neither Hagel nor Dempsey confirmed whether the Islamic State’s reclusive leader, Abu Bakr al-Baghdadi, had been killed or injured in weekend strikes. The group on Thursday issued an audio statement purporting to be Baghdadi’s voice.

U.S. airstrikes continue in Syria, primarily against the Islamic State. On Thursday, U.S. aircraft struck an al-Qaeda-linked militant cell called the Khorasan group, according to Maj. Curtis Kellogg, a spokesman for the U.S. Central Command. It marked only the third time U.S. forces have targeted the group, which officials believe has been conspiring to stage attacks in the West.