Iraqi forces battled militants northeast of Baghdad Friday, as Washington said a powerful "jihadist" group (ISIL) was beyond anything it has seen and that operations in Syria may also be needed.

Iraqi forces battled militants northeast of Baghdad Friday, as Washington said a powerful "jihadist" group (ISIL) was beyond anything it has seen and that operations in Syria may also be needed.

Pentagon chiefs warned of the dangers of ISIL as the West reeled from the grisly execution of American journalist James Foley.

But despite the ISIL's threat to kill a second reporter if it does not halt air strikes, Washington confirmed it had again bombed the militants in northern Iraq.

Iraqi government troops and Kurdish forces launched an operation on Friday aimed at retaking the Jalawla area of Diyala province, northeast of the capital, from militants who seized it on August 11, officers said.

The operation came after Pentagon chiefs said that defeating ISIL, which spearheaded an offensive that overran swathes of Iraq, will require efforts across the region, including in neighboring Syria, where the "jihadists" also control large areas.

"They marry ideology and a sophistication of strategic and tactical military prowess," Defense Secretary Chuck Hagel said of the "barbaric" militants.

"They are tremendously well funded. This is beyond anything we have seen."