Defense Secretary Chuck Hagel said U.S. military intervention in Iraq will continue for some time because the Islamic State of Iraq and Syria will not be defeated quickly.

“We’re very clear-eyed about this,” Hagel told reporters Thursday. “We’re pursuing a long-term strategy because [ISIS] poses a long-term threat.”

U.S. airstrikes in Iraq, he said, have blunted ISIS’s momentum but he expected it to “regroup” and use its vast resources to try to kill more Americans and take over more territory in the Middle East.

Just two days after ISIS released a video of the beheading of an American journalist and one day after the U.S. confirmed that it launched a failed mission in Syria to rescue James Foley and other ISIS hostages, Hagel said ISIS poses an imminent and very dangerous threat to Americans.

“They’re beyond just a terrorist group,” he said. “They are tremendously well-funded ... this is beyond anything that we’ve seen. We must prepare and the only way you do that is to take a cold, steely, hard look at it and get ready.”