By mid-November 2016, it was reported that since the start of the fighting in Deir ez-Zor city five years earlier, around 3,000 anti-government jihadists and 2,500 pro-government fighters had been killed.

[16] The rebel units in eastern Syria were originally largely independent and unorganized, until many accepted the authority of the National Coalition for Syrian Revolutionary and Opposition Forces (SNC) in late 2012.

Large swaths of the province fell into rebel hands after the alliance between the ruling Alawite elite and Sunni tribes collapsed, leaving government troops with stretched supply lines.

[31] On 24 June, government forces shelled residential areas of the city for the second day, killing at least 20 people, following which the military withdrew to the outskirts.

[33] On 28 June, it was reported that the opposition almost entirely controlled the city of Deir ez-Zor, while the military continued its intense shelling, trying to take it back.

[48] A rebel commander in the area also told Reuters that only one army outpost and an artillery position still remained under the control of the Syrian government near Mayadin.

[50] On 9 August, it was also claimed by British humanitarian Peter Clifford that the Syrian Armed Forces only had three army outposts remaining in the province's countryside and that they were being attacked.

Shortly afterwards video of its downing was released on YouTube and Syrian opposition and Israel Radio sources the pilot was captured by the rebels.

[52] SANA later confirmed its lost warplane, insisting the plane was not shot down, but rather alleging technical problems which forced it to crash-land and the pilot to eject.

Most government departments have shut and public workers are unpaid in what activists call collective punishment of a tightly knit population siding increasingly with rebels after alliances between the Damascus elite and tribal chiefs unraveled.

[56] On 22 August, the AFP reported that the FSA seized parts of the city of Abu Kamal, including an intelligence office and military checkpoints.

[67] On 30 November, SOHR reported that government troops abandoned the Omar oilfield east of Deir ez-Zor, which was soon occupied by opposition forces.

[68] On 22 November, after 20 days of siege rebels also captured the Mayadin military base from which soldiers evacuated to Deir ez-Zor airbase, thus forcing out any government elements from area spanning from Iraqi city to capitol of the province.

[70] On 3 December, fierce combat broke out in the Mouzafin and Joubaila districts of Deir ez-Zor, while rebels reportedly shelled the nearby military airbase.

[71] On 12 December, the French Aid agency, Médecins Sans Frontières called for sick and wounded people to be evacuated from the besieged city.

SOHR director, Rami Abdel Rahman claimed that "Siyasiyeh bridge is the most important in the area as it connects Deir ez-Zor to Hasakah.

"[73] Elsewhere in Deir ez-Zor, activists claimed that rebels had also taken control of a government intelligence complex after five days of heavy fighting, with assistance from Islamist fighters.

[78] On 2 May 2013 the Deir ez-Zor suspension bridge, built during the Mandate for Syria and the Lebanon period (1920−1941), was destroyed by shelling from the Free Syrian Army.

[79] On 6 May, the Free Syrian Army shot down a SAA helicopter and killed eight government soldiers near Deir ez-Zor military airport.

[citation needed] On 22 June, violence reignited between rebel and regular forces at the Mashfa al-Qalb (heart hospital) checkpoint of Deir ez-Zor city.

The FSA-affiliated Ahfad al-Rasul Brigade, recently supplied by Qatar with anti-aircraft missiles, played an important role in taking Hawiqa.

[90] On 27 December, rebel fighters seized control over the majority of the town of Al-Jafra, strategically adjacent to the Deir ez-Zor Military Airbase.

[95] On 27 March, the rebels blew up a building in the al-Rasafa neighborhood of Deir ez-Zor city with confirmed casualties in the ranks of the Syrian Army.

[97] This marked the beginning of a two-month offensive that ended when, on 14 July, ISIS held all rebel-controlled neighborhoods in the provincial capital after expelling Nusra and other rebel groups.

[100] On 17 August, SOHR said that in the two previous weeks Islamic State (IS) jihadists killed over 700 tribal members in eastern Syria in the oil-rich Deir ez-Zor Governorate.

[102] Two days later, General Issam Zahreddine returned to Deir Ezzor with a convoy of 600 Republican Guard soldiers and 90 armed vehicles to reinforce the military airport defense.

Government troops also continued their offensive against Sakr Island in an attempt to create a buffer zone between ISIS-held areas and the old military airport.

[114] ISIS suffered more casualties on 20 November after the 104th Brigade attacked their supply bases, sniper hideouts and repelled infiltration attempts.

[119] On 5 December, the Army launched a counter-attack and recaptured parts of Al Mari'iyah village[118] and regained control of perimeter the Deir ez-Zor airbase from ISIS.

ISIS also pulled back from the heights overlooking Deir ez-Zor after it was exposed to heavy aerial bombardment, which reportedly used chlorine.