The K1 Air Base is the third site coalition forces have left this month, in line with U.S. plans to consolidate its troops in two locations in Iraq.

With ISIS in retreat, the Kurdish-led Syrian Democratic Forces and the Syrian government have been in a race to secure parts of the oil-rich Deir el-Zour province.

With more than a thousand militants killed and territory slipping away, the Islamic State group is losing its grip on the Syrian border town of Kobani under intense U.S.-led airstrikes.