After a deadly weekend of fighting saw hundreds killed or kidnapped, ISIS continued to amass gains in Deir Ezzor Province today, using a sandstorm which was hampering visibility to launch attacks against government forces on several fronts.

Several towns and villages in the province, centering around the city of Deir Ezzor, fell to ISIS, who also captured much of a major arms depot in Ayash. The sandstorm allowed them to advance without concern about Syrian and Russian warplanes opposing them.

ISIS has held virtually the whole Deir Ezzor Province for over a year, with the exception of the capital city, and the nearby airbase. The province is the primary route by which ISIS connects its capital city of Raqqa to its territorial possessions in Iraq.

ISIS has lost ground to the Syrian military elsewhere in the country in recent months, and lost some territory to Iraq in Ramadi. This new push seems to be an effort to get the momentum back on their side, and in a war that has seen momentum shift several times already, it may well happen.