As the Islamic State’s once-vast swathe of territory shrinks across Syria and Iraq, Deir al-Zour province has become a hub for the group’s senior leaders. Stretching along the eastern border with Iraq, it has also become a geopolitical battleground for forces trying to support or thwart Iranian attempts to secure supply routes stretching from Beirut to Tehran.

While SDF fighters have advanced against Islamic State positions on the eastern bank of the Euphrates River, forces allied to President Bashar al-Assad’s government have scythed through the extremist group’s territory from the western side, bringing the rival offensives to within several miles of each other.