As US warplanes kept up attacks on Sunni militants in Iraq yesterday, US military and civilian officials said it was not possible to defeat the Islamic State unless the US or its allies took them on in Syria, The Boston Globe reported.
General Martin Dempsey, chairman of the Joint Chiefs of Staff, said this was an organisation that had an apocalyptic end-of-days strategic vision that would need to be defeated.
Dempsey said at a joint news conference with defence secretary Chuck Hagel that this would not necessarily require airstrikes by the US, but Hagel appearing to leave open that possibility said, ''We're looking at all options.''
According to the US military, the Islamic State had a highly mobile force numbering possibly 17,000 fighters and could move across the Iraq-Syria border with impunity.
Taking on the militant group, US warplanes conducted six more strikes on Islamic State targets near the Mosul Dam, the Pentagon said yesterday. Three Humvees, another vehicle, and several improvised explosive device emplacements were destroyed in the attack.
The attacks brought to 90 the number of airstrikes conducted by the fighter jets, drones, and bombers that the US had pressed against the Sunni militants since president Obama authorised the strikes.
General Dempsey however struck a measured note while describing the sort of broad effort that would be needed roll back ISIS in Syria and Iraq.
Meanwhile, Syrian government forces captured Mleiha, a suburb east of Damascus, after five months of heavy fighting.
President Obama had talked about Iraq at the White House on Saturday, but was yet to detail a plan for rolling back ISIS' gains.
"It requires a variety of instruments, only one small part of which is airstrikes," he said. "I'm not predicting those will occur in Syria, at least not by the United States of America. But it requires the application of all of the tools of national power - diplomatic, economic, information, military."
According to commentators, general Dempsey's comments were notable as he was the president's top military adviser and had been among the most outspoken in describing the risks of ordering airstrikes in Syria when the civil war there began.
In the current battle with ISIS inside Iraq, Obama's military strategy had been focused on containing the militant organisation rather than defeating it, Defense Department officials and military experts said.