U.S. Defense Secretary Chuck Hagel has said the militant group Islamic State (IS) poses an "imminent threat" to U.S. interests and "must be defeated."
Speaking to reporters in Washington on August 21, Hagel said IS was more than a traditional "terrorist group," and better armed, trained and funded than any recent threat.
Appearing alongside Hagel, the chairman of the U.S. Joint Chiefs of Staff, General Martin Dempsey, said it was possible to contain the IS militants, but cautioned it can't be done permanently without going after the group in Syria.
Dempsey said he wasn't predicting U.S. air strikes in Syria. However, Hagel said all options were on the table.
The press conference comes two days after IS released a video showing the beheading of U.S. journalist James Foley, who had been held hostage in Syria for two years.
The U.S. Justice Department announced on August 21 that it is opening a criminal probe into Foley's death.
It also emerged on August 21 that IS militants had demanded $132.5 million -- or 100 million euros -- in ransom for his release.
Hagel said the killing of Foley along with the group's other actions show they are "an imminent threat" to U.S. interests in Iraq and elsewhere.
The threat is "beyond anything we have seen," Hagel said.
Hagel said he regretted the failure of a clandestine mission to rescue Foley and other U.S. hostages from Syria, and vowed not to relent in efforts to bring home U.S. citizens.
The U.S. military has stepped up air strikes on IS targets in northern Iraq.
IS has threatened to kill another captured U.S. journalist -- identified as Steven Joel Sotloff -- if the United States does not halt the strikes.
Hundreds of thousands of Iraqi civilians have been driven out of their homes as IS and its Sunni militant allies continue to advance through much of north and west Iraq.
According to the International Organization for Migration, more than half a million Iraqis have fled their homes since Islamic State began their offensive in June.
Meanwhile, Iraqi Prime Minister-designate Haidar al-Abadi has called on Iraqi Christians not to leave the country.
"Christians are urged not to migrate and to stay in the homeland because they are a key component of the country," he said following a meeting on August 21 with Christian clerics.
With reporting by AP, Reuters and AFP