After a string of defeats, ISIL has been pushed out from most of the territory it captured in 2014.
ISIL has lost further ground in Iraq and Syria as the armies of both countries and the Syrian opposition squeeze its forces.
Iraqi forces took full control of the city on the Syrian border after seizing the last border crossing held by ISIL, or the Islamic State of Iraq and the Levant group.
They have been getting help from Sunni tribal fighters and the Popular Mobilisation Forces (PMF), a Shia paramilitary force.
Just five months ago, ISIL still controlled vast expanses of territory, including major cities, on both sides of the Iraq-Syria border.
Since then, it has been driven out of Mosul in Iraq and its self-declared capital Raqqa and Deir Az Zor in Syria.
The fighters now only control a chunk of territory in Iraq’s northwest, along the Syrian border.
Earlier on Friday, Syria’s army said it was in control of Deir Az Zor, the capital of an oil-rich eponymous region that was crucial for ISIL’s finances.
The campaign to retake the eastern city began in September when government forces managed to break the three-year siege of the eastern Syrian city by ISIL.
Al Jazeera’s Hashem Ahelbarra, reporting on Friday from Gaziantep on the Turkey-Syria border, said Syrian forces will most probably find a city destroyed by months of air raids and intense fighting.
“This is a significant development in that it paves the way for the Syrian army to start expanding further in the eastern part of the country,” he said.