September 5, 2017 one of the longest sieges in modern history ended, and Dair al-Zoor was liberated.
Since the end of 2013, rebel forces surrounded Deir ez-Zor and captured half of the city and almost the entire province. ISIS became increasingly involved in the battle. The following rebel infighting in and near the city resulted in ISIS retreating from Deir ez-Zor in February 2014.
In April 2014, following their defeat at the hands of the rebels, ISIS returned and launched a large-scale offensive against the Syrian rebel groups in the Deir ez-Zor Province, expelling them from the area, and allowing ISIS to gain control of most of the Deir ez-Zor Governorate and besiege the remaining Syrian Government forces, in July 2014.
During the siege 4000 soldiers spent 1400 days under siege by over 15,000 ISIS terrorists. Defending themselves and their points against daily suicide attacks and raids.
The siege witnessed many attempts by ISIS to brach the military base, while the city’s power and water supply were almost totally destroyed.Up to 480 defenders, 1800 Jihadists, and 500 civilians were killed, while hundreds of civilians were abducted and most are still missing.
On 27 August, the Syrian Army launched a major offensive along the Sukhna-Deir ez-Zor highway, advancing to positions 66 kilometers from Deir ez-Zor city by 29 August. On 31 August, the Syrian Army’s Tiger Forces established full control over the strategic mountain of Bishiri, west of Deir ez-Zor. The offensive was accompanied by heavy Russian airstrikes on ISIL positions. They also captured the town of Haribshah. At this point, Syrian Army troops were 50 kilometers from Deir ez-Zor.
By 2 September, the Syrian Army’s Tiger Forces and 5th Corps alongside the Iran-backed Afghan Shia militia Liwa Fatemiyoun advanced from mount Bishiri towards Tal Al-Abd, Jabal Nazerat, Jabal Nairaman, and Jabal Admah, resulting in the capture of those hilltops and placing the Syrian Army within 25 km (16 mi) of lifting the siege imposed by ISIS for years on Deir ez-Zor city and within 16 km of village of al-Shulah, located southwest of the city. The next day, the Tiger Forces progressed further eastwards, coming within 18 km of Deir ez-Zor, capturing some minor hills in the desert and later in the day advancing towards al-Shulah and imposing fire control over the village from the north by securing Mount Neerman.
By 4 September, Syrian Army troops were within three kilometers of Deir ez-Zor, as ISIL sent reinforcements from Mayadin. The 5th Corps alongside the 18th Reserve Division captured the town of Kabajib during midday and later in the day captured the town of al-Shulah alongside the Tiger Forces.
The siege of the city was broken on 5 September 2017, at around 2 P.M. local time, when Syrian Army troops met the 137th Brigade on the western outskirts of the city.