WASHINGTON - President Barack Obama acknowledged that U.S. intelligence agencies underestimated the threat from Islamic State militants and overestimated the ability and will of Iraq's army to fight.

Questioning Obama's strategy to destroy the group, House Speaker John Boehner said the U.S. may have "no choice" but to send in American troops if the mix of U.S.-led airstrikes and a ground campaign reliant on Iraqi forces, Kurdish fighters and soon-to-be trained Syrian rebels fails to achieve that goal.

Boehner, in an interview broadcast Sunday, did agree with the White House that Obama had the power to order airstrikes in Iraq and Syria, but said he believes Congress should consider a resolution authorizing the use of force for this specific mission.

Boehner, R-Ohio, said he would bring lawmakers back to Washington - they are not set to return until after the Nov. 4 election - if Obama were to seek such a resolution.

Obama described the U.S. intelligence assessments in response to a question during a CBS "60 Minutes" interview that was airing Sunday night. He was asked about how Islamic State fighters had come to control so much territory in Syria and Iraq and whether it was a surprise to him.

The president said that during the Iraq war, U.S. military forces with the help of Iraq's Sunni tribes were able to quash al-Qaida fighters, who went "back underground."

"During the chaos of the Syrian civil war, where essentially you have huge swaths of the country that are completely ungoverned, they were able to reconstitute themselves and take advantage of that chaos," Obama said, according to an excerpt release before the show aired.

He noted that his director of national intelligence, James Clapper, has acknowledged that the U.S. "underestimated what had been taking place in Syria." Obama also said it was "absolutely true" that the U.S. overestimated the ability and will of the Iraqi army.

The Obama administration has cited its intelligence weaknesses before.

At an August news conference, he said "there is no doubt" that the Islamic State group's advance "has been more rapid than the intelligence estimates" suggested it would be.

U.S. intelligence agencies, he said, did not have "a full appreciation of the degree to which the Iraqi security forces, when they're far away from Baghdad, did not have the incentive or the capacity to hold ground against an aggressive adversary."

At an intelligence conference this month, National Security Agency Director Mike Rogers expressed regret that his agency had not been "a little stronger" in tracking the Islamic State's shift "from an insurgency to an organization that was now focused on holding ground, territory, the mechanism of governance."

Obama called Syria ground zero for jihadis around the world, and said military force was necessary to shrink their capacity, cut off financing and eliminate the flow of foreign fighters.

He had been less adamant about the threat in the past. In an interview published early this year by The New Yorker, Obama appeared to minimize the Islamic State group militants by comparing it to a junior varsity basketball team. The White House at the time said he was speaking about a different threat posed by a range of extremists across the world.

The White House pushed back against Boehner's comments on ABC's "This Week" about the potential need for American ground troops to confront the militants.

Asked whether he would recommend sending in Americans if no one else was able to step up, Boehner said, "We have no choice. These are barbarians. They intend to kill us. And if we don't destroy them first, we're going to pay the price."

But Obama's deputy national security adviser, Tony Blinken, said the country would not see a repeat of the Iraq war.

"Hundreds of thousands of Americans on the ground in the Middle East getting bogged down, that's exactly what al-Qaida wants," Blinken said. "That's not what we're going to do."