Conversely, the United States overestimated the ability of the Iraqi army to fight the militant groups, Obama said in a 60 Minutes interview taped on Friday, days after the U.S. president made his case at the United Nations for action.
Earlier Sunday, U.S.-led airstrikes hit three oil refineries near Syria's border with Turkey early Sunday in the ongoing offensive against Islamic State militants.
The Britain-based Syrian Observatory for Human Rights said the attacks occurred shortly after midnight, adding that they also hit a plastics factory.
Citing US intelligence
In the CBS interview, citing earlier comments by Director of National Intelligence James Clapper, Obama acknowledged that U.S. intelligence underestimated what had been taking place in Syria.
Islamic militants went underground when U.S. Marines quashed al-Qaida in Iraq with help from Iraq's tribes, he said.
“But over the past couple of years, 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 a clip of the interview broadcast earlier.
“And so this became ground zero for jihadists around the world," he said.
Obama last week expanded U.S.-led airstrikes, which began in Iraq in August, to Syria and he has been seeking to build a wider coalition effort to weaken Islamic State.
This group has killed thousands and beheaded at least three Westerners while seizing parts of Syria and northwestern Iraq.
Washington Post interview
Clapper told a Washington Post columnist this month that U.S. intelligence had underestimated Islamic State fighters and overestimated Iraq's army.
“I didn't see the collapse of the Iraqi security force in the north coming,” Clapper was quoted as saying. “I didn't see that. It boils down to predicting the will to fight, which is an imponderable.”
Obama outlined the military goal against the Islamic State group: “We just have to push them back, and shrink their space, and go after their command and control, and their capacity, and their weapons, and their fueling, and cut off their financing, and work to eliminate the flow of foreign fighters.”
But Obama said a political solution is necessary in both Iraq and Syria for peace in the long term, according to the interview, which will be broadcast in full on Sunday night.
US Congress reaction
Also on Sunday, U.S. lawmakers stepped up calls for congressional authorization of Obama's war against Islamic State militants in Iraq and Syria, amid signs the United States and its allies face a long and difficult fight.
U.S. House Speaker John Boehner of Ohio told ABC's This Week that he believed Obama had the legal authority for strikes against Islamic State militants, but would call lawmakers back from their districts if Obama sought a resolution backing the action.
“I think he does have the authority to do it. But ... this is a proposal the Congress ought to consider,” Boehner said, warning that the United States could eventually be dragged into another ground war in the region.
Obama and other U.S. officials have said they believe no further vote to authorize force is needed, but political analysts warn that the war could dampen participation by anti-war Democrats in the November elections.
Senator Chris Murphy, a Connecticut Democrat and member of the Senate Foreign Relations Committee, told CNN that Congress should debate the issue because of uncertainty about how long the U.S. military would remain engaged in Syria.
“There are some serious questions that we have to ask,” Murphy said. “You need a realistic political strategy. And I just don't think we have that today in Syria.”
Senator John Barrasso, a Wyoming Republican and member of the Foreign Relations Committee, urged Obama to follow the lead of British Prime Minister David Cameron in recalling the British parliament.
“I think the president has an obligation to call us back tomorrow to start this debate,” Barrasso said.
- Syrian Information Minister Omran al-Zoubi said a recent United Nations resolution that bans travel to fight with religious extremists is a "political victory" for Syria. Washington has insisted that the air campaign against Islamic State fighters that began last week would not benefit the Syrian regime, now three years into a civil war.
- Activists and Kurdish officials said Islamic State fighters fired rockets into the town, known both as Kobani and Ain al-Arab. At least 12 people were reported wounded in the rocket attacks, while no immediate casualty estimates were released for the coalition strikes.
- Britain's Defense Secretary Michael Fallon said Sunday armed British warplanes are flying daily missions over Iraq and would launch airstrikes if called in by local forces on the ground.