[76] The SDF launched their ground operation on 8 September 2017 by attacking ISIL-held villages in the northern Deir ez-Zor countryside;[77][78] on the next day, the campaign was officially announced in the al-Shaddadah Subdistrict, with the stated aim of expelling ISIL from all areas north and east of the Euphrates river.

[82][83] On 12 and 13 September, the SDF captured several locations at Deir ez-Zor's northern entrance (including the former Brigade 113 and al-Niran Battalion bases, the Sadkob station and part of the sheep market)[84] as well as the silos and cotton storages in the Industrial City.

[123] Many SDF fighters were killed and executed on 15 October after ISIL attacked their positions on the provincial border between al-Hasakah and Deir ez-Zor, infiltrating several checkpoints and outposts along the main road between Al-Salhiyah and Sor.

[125] Laila al-Abdullah, the spokesperson of the SDF, announced that they had captured the al-Omar oil field after a military operation in early hours of 22 October, and were clashing with ISIL fighters in an adjacent housing complex.

[138] The United States Department of Defense (U.S. DoD) later announced in February 2018 that Shaykh Abu Anas al-Furati, a senior ISIL commander, was killed in an airstrike on Hajin on 27 November 2017.

[140][141] The Deir Ez-Zor Military Council reported on 12 December that their forces had captured several towns along the eastern bank of the Euphrates, including Hasiyat, Jayshiyah, Jadleh, al-Bahrah, and Gharanij after a brief battle.

[190] On 10 September, the SDF began to advance from 4 different fronts towards the areas controlled by ISIL – the pocket with Hajin, al-Susa, al-Shafa, and the neighboring villages straddling the eastern banks of the Euphrates river.

[195] The next day, ISIL conducted multiple SVBIED attacks on SDF positions in al-Baghuz Fawqani, reportedly killing and injuring scores of SDF-affiliated Kurdish fighters, with a heavy firefight occurring soon after.

[200] On 20 October, the SOHR stated that the US-led coalition had carried out two "massacres" via airstrikes in al-Susah, resulting in the deaths of 58, including 41 civilians, with ISIL only receiving 11–17 casualties in the strikes; 10 children were also reported to have been killed.

[208] ISIL continued its counterattack on 29 October with the group retaking control of the towns of Marshidah, Mouzan, Safafinah, Shajlah, and Baghouz al-Fawqani as well as al-Susah from the SDF, forcing the Kurds to retreat after becoming overwhelmed.

[213] On the same day, the Iraqi Al Mada newspaper reported that the Popular Mobilization Forces had crossed into Syrian territory and seized 30 fortified border posts in areas previously abandoned by the SDF after the 26 October ISIL counterattack.

[215][216] During the intermediary period of halted ground operations, the coalition had continued a heavy bombardment campaign targeting ISIL fighting positions, tunnels, mortars, staging areas, and weapons caches.

[226] On 6 December, Redur Khalil, an SDF commander, confirmed their forces had pushed into Hajin and had taken portions of the town, including some neighborhoods and a mosque, but not the hospital, amidst ongoing heavy clashes.

[227] The Coalition stepped up airstrikes to support the SDF's advance, with a 5 December press release[228] detailing multiple strikes conducted near Hajin targeting ISIL supply routes, tunnels, fighting positions and trucks.

[233] US Special Presidential Envoy to the anti-ISIL Coalition Brett H. McGurk said "We've gotten to a point where almost every ISIS fighter is wearing a suicide vest, the extent of IEDs and placements, it's very, very difficult fighting and so it's taking some time.

[238][239] By dawn on 14 December, SDF forces – spearheaded by the Kurdish YPG – fully captured Hajin as ISIL defenses collapsed, due to an intensified ground push supported by increased Coalition airstrikes.

[241] Europe-based activist Omar Abu Layla stated that disagreements among ISIL ranks over hierarchy between Iraqi and Syrian fighters helped speed up the collapse of the extremist group's defenses in the town.

[242] SOHR added that since the launch of the third phase of the Deir ez-Zor campaign on 10 September, 922 ISIL gunmen, 539 SDF fighters, and 324 civilians – of which were 113 children and 72 women – had died in the deadly fighting for the enclave.

[244] With the capture of the Hajin stronghold – the Islamic State's last de facto capital – on 14 December, ISIL fighters retreated to the remaining rural villages still under their grasp within the pocket.

[18] The U.S. estimated there were still a diehard contingent of 2,500 ISIL fighters entrenched within the remaining enclave as the Islamic State still controlled the villages of Al-Susah, Al-Marashidah, Al-Shaafah, al-Baghuz Fawqani, al-Shajla and surrounding settlements.

The loss of al-Susah was a heavy blow against the Islamic State, as the terrorist organization's territorial control in the pocket had dwindled to four key towns: Al-Marashidah, Mozan, al-Shajlah, and as-Safafinah (though clashes still continued at Al-Baghuz Fawqani).

[269] The civilian exodus continued, as SDF and Kurdish social media accounts posted pictures reportedly showing the relatives of Islamic State fighters fleeing; many of them included nationals from France, Pakistan, Iraq, and Turkey.

[273] Zana Amedia, an SDF spokesman, attributed their ground momentum in recent weeks to a change of investment tactics after their frontlines collapsed in late October 2018, due to an aggressive ISIL counterattack during a sandstorm.

The capture of Baghuz Fawqani prompted the SOHR to proclaim the imminent defeat of ISIL in Deir ez-Zor, with the jihadist group only possessing 10 square km of remaining territory in the Middle Euphrates Pocket, and the remainder of their die-hard combatants holed up in scattered homesteads among the irrigated fields and orchards on the north bank of the valley.

[270] On the same day, the villages of as-Safafinah and al-Shajlah were also reported to have been overrun by the SDF backed by heavy French and American shelling, leaving al-Marashidah as the last stronghold in ISIL's grip – merely 0.01 percent of the territory its self-proclaimed caliphate once held.

[278] During ISIL's attempted breakout, Syrian Arab Army units that had deployed across the river targeted the Islamic State's poorly established positions at the town as well, indirectly assisting the Kurds.

[316] The SDF reported the deaths of 37 ISIL members, along with the destruction of 19 locations, one enemy motorbike, four roads, one mortar, and one weapons cache in the preemptive airstrikes leading up to the assault, while only losing two of their own.

Attrition became a larger factor as the surrounded jihadists were letting their families, other hostages, and more expendable fighters leave due to dwindling food resources from the SDF's encirclement, with hundreds of civilians and dozens of surrendering militants regularly flowing out of the enclave.

A number of the fleeing wives were interviewed by international media, giving accounts of their journey to and conditions under ISIL's "caliphate", some describing how they lived in dug-up holes with hoisted tents to protect against airstrikes.

[342] As well as bolstering its propaganda efforts,[225] many scattered ISIL fighters and loyalist sleeper cells melted into the local populace and continued terror bombings and attacks, prompting major counterinsurgency operations.