The United States is looking to keep pressure on jihadist militants in Iraq, launching air strikes after the murder of a journalist underlined the international threat.
Meanwhile, in the latest sign that a reluctant America could be dragged deeper into the fighting, officials revealed on Thursday that US special forces had already carried out a failed hostage rescue mission inside Syria.
On Tuesday, the Islamic State of Iraq and the Levant (ISIL), also known as ISIS or Islamic State, released a video in which a militant with a British accent is seen beheading American journalist James Foley and threatening a second US hostage.
The murder has stoked fears that the territory seized in Syria and northern Iraq could become a launching pad for a new round of global extremist attacks.
US President Barack Obama called on countries in the region to come together to "extract the cancer" of the ISIL jihadist ideology, and on Thursday US strikes continued.
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In six bombings near a dam north of Mosul, US warplanes damaged three Humvee armoured trucks, another vehicle and several roadside bomb "emplacements", Central Command said.
The US military has conducted 90 air strikes in Iraq since August 8, including the latest raids. Of those operations, 57 have been in support of Iraqi government forces near the Mosul dam.
Separately, officials confirmed that in recent months US special forces had carried out a raid inside eastern Syria to try to rescue people held hostage by ISIL militants, reportedly including Foley.
"This operation involved air and ground components and was focused on a particular captor network," Pentagon spokesman Rear Admiral John Kirby said.
"Unfortunately, the mission was not successful because the hostages were not present at the targeted location."
In the execution video - released online by the ISIL - a black-clad militant said that Foley, a 40-year-old freelance journalist, was killed to avenge US air strikes against the group.
The man then paraded a second US reporter, Steven Sotloff, before the camera and said he, too, would die unless Obama changes course.
Foley was kidnapped in northern Syria in November 2012 and his grisly murder provoked global revulsion and condemnation.
On Thursday, US Attorney General Eric Holder, noted that the FBI had an open criminal probe into Foley's kidnap.
"We have long memories and our reach is very wide. We will not forget what happened and people will be held accountable - one way or the other," he said.
