(CNN) -- The Syrian army and allied forces have taken full control of the city of Deir Ezzor, the last major Syrian city in ISIS' hands, Syria's Defense Ministry and state media said Friday.
"Syria's Army in cooperation with allied forces liberated the entire city of Deir Ezzor from the ISIS after killing a large number of the terrorists, among them foreigners," the Syrian Defense ministry said in a statement.
"The Syrian Arab Army restored security and stability to the entire city of Deir Ezzor after eliminating Daesh's last stronghold in it," Syrian state media said, using an Arabic name for ISIS.
The city's seizure represents a highly significant gain for Syria's government and a big blow for ISIS.
Two Syrian government enclaves in the city's west were besieged by ISIS for more than three years before the terror group was ousted about two months ago by the Syrian military backed by Russian forces.
Syrian and allied forces have since battled to push ISIS from its final holdouts in the city.
ISIS' defeat in Deir Ezzor follows its fighters' loss of Raqqa -- the de facto capital of the so-called ISIS caliphate -- last month to US-backed militias. ISIS still holds positions in a number of towns and villages in Deir Ezzor province, near the Iraqi border in eastern Syria.
Deir Ezzor holds particular significance for Syria's government, in part because the city held many hard-line extremists even before the 2011 uprising against President Bashar al-Assad.
Positioned deep in ISIS' heartland, the Syrian government considered the city more of a hub for the extremist group than Raqqa. At the same time, the plight of the besieged Syrian forces and civilians gained an almost mythical status for many pro-government Syrians.
From April 2016 until September this year, when ISIS' siege in Deir Ezzor was broken, the United Nations' World Food Programme had to use high-altitude airdrops to deliver vital food and humanitarian supplies to nearly 100,000 people trapped in the government enclaves.
At one point, US forces accidentally bombed Syrian forces in Deir Ezzor, resulting in serious casualties and some ISIS advances, later reversed by the Russian air force. This incident made Deir Ezzor central to the Russian, pro-Assad and Iranian narrative that the United States was actually aiding ISIS.
The seizure of so much of ISIS's heartland in eastern Syria has also given a major morale boost to the Russian-backed Syrian army, showing that it has gained the upper hand in the Syrian civil war.
At the same time, Deir Ezzor is extremely important to the Russians as evidence that their strategy in Syria is working and that they are really combating ISIS. Its capture indicates that the Syrian government will have a major claim to large parts of Syria, rather than the US-backed Syrian Democratic Forces, who took Raqqa.
The region also holds economic importance. The Euphrates Valley is home to some of Syria's most important farm land, especially for cotton, as well as a number of oil fields.