QAIM, Iraq -- The US-led coalition's newest outpost in the fight against the Islamic State group is in a dusty corner of western Iraq near the border with Syria. Here, several hundred American Marines operate close to the battlefront, a key factor in the recent series of swift victories against the extremists.

The Americans directed Iraqi troops in their victory last week recapturing the nearby border town of Qaim, the militants' last urban holding. Now the Marines will lead the equally difficult task of clearing the extremists from their last redoubt: a large stretch of empty desert north of the Euphrates River adjoining the border with Syria.

They also face the possibility of friction with Iranian-backed Iraqi Shiite militias that are increasing their own presence in the border region.