US President Barack Obama came under fire Sunday from Republican lawmakers, who warned that a debacle in Iraq will give Islamist extremists a staging area for "the next 9/11."
Senator Lindsey Graham, a proponent of US air strikes, also called for the resignation of Iraqi Prime Minister Nuri al-Maliki and direct US engagement with Iran on the crisis set off this week by a lightning offensive by the Islamic State of Iraq and the Levant (ISIL) jihadist group.
Fighters from the group routed the much larger Iraqi army, seizing the country's second largest city Mosul and sweeping through the Sunni heartland towards Baghdad.
The United States moved an aircraft carrier and two missile-guided warships into the Gulf on Saturday as Obama weighed his options.
Retired military officers questioned whether air strikes were a viable near-term option with no US forces on the ground to provide precise targeting data.
Retired General Peter Chiarelli, a former commander in Iraq, said ISIL fighters "have an opportunity here, they have taken advantage of that opportunity, and I think we should really, really be concerned."
"I read someplace yesterday, where they're the richest terrorist group in the world after what they were able to seize in Mosul, so I'm concerned, and I think all Americans should be concerned," he told ABC's "This Week."
Graham, interviewed on CNN's "State of the Union," said Washington had to act "because Iraq and Syria combined are going to be the staging area for the next 9/11 if we don't do something about it."
"The people holding ground in Iraq also hold ground in Syria. Economic instability that comes from a collapsed Iraq will affect gas prices and our economic recovery," he said.
Another Republican lawmaker, House Homeland Security chairman Michael McCaul, stopped short of calling for US military action but pressed for an intensive diplomatic initiative with US allies in the region to find a political solution involving Iraq's Sunni, Shia and Kurds.
"Without their cooperation against the extremists this isn't going to happen. They're not going to do it on their own. They need us to lead them and we're not leading right now as a nation," he said on ABC's "This Week."
"This is the worst of the worst," he said of ISIL. "If they get back into the United States or western Europe, I see that as the biggest threat today."