But the chairman of the Joint Chiefs of Staff said that right now, he still believes the insurgent group is still more a regional threat and is not plotting or planning attacks against either the US or Europe.
Speaking on a military plane en route to Afghanistan yesterday, Dempsey provided more detail into his thinking about the Islamic militants who have stormed across Iraq, operating out of safe havens in Syria.
The group took over Iraq's second largest city, Mosul, in June, and has since declared an Islamic state, or caliphate, in territory under its control in Iraq and Syria.
Dempsey also told reporters traveling with him that he believes that key allies in the region including Jordan, Turkey and Saudi Arabia will join the US in quashing the Islamic State group.
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He contrasted the Islamic State group to the Yemen-based al-Qaida in the Arabian Peninsula, which has plotted and attempted attacks against the US and Europe. As a result, the US has conducted counterterrorism strikes against the group within Yemen.
Dempsey said that so far, there is no sign that the Islamic State militants are engaged in "active plotting against the homeland, so it's different than that which we see in Yemen."
He added that those regional partners could come together and squeeze the Islamic State group "from multiple directions in order to initially disrupt and eventually defeat them. It has to happen with them, much less with us.