The battle of Zinjibar was fought between Yemeni government forces and the Islamist militant group Ansar al-Sharia in and around Zinjibar, the provincial capital of Abyan governorate. As the state was preoccupied with the Yemeni revolution, the resultant security vacuum in southern Yemen was capitalized on by al-Qaeda in the Arabian Peninsula (AQAP), which used a local insurgent front in Ansar al-Sharia to seize territory for the first time.

Using the nearby town of Jaar as a staging ground, Ansar al-Sharia invaded Zinjibar on 29 May 2011 and captured it relatively unopposed. Most security forces fled except for the 25th Mechanized Brigade, which was besieged at its base near the city. Reinforcements were brought in but were met with fierce resistance and a tightened siege on the brigade. The army partnered with the local tribes to launch an offensive on 17 July, which culminated in the relieving of the 25th Mechanized Brigade and the capture of eastern Zinjibar on 10 September. Clashes continued into the next year with Ansar al-Sharia maintaining control over most of Zinjibar.

In response to renewed military pressure, Ansar al-Sharia launched two raids on army installations near Zinjibar on 5 March 2012 which killed and wounded hundreds of soldiers. The battle intensified thereon, with army forces making inroads into Zinjibar in late April. On 12 May, the government initiated a large-scale offensive to recapture all territory occupied by Ansar al-Sharia. Army forces conducted an arc-shaped advance upon Zinjibar, pushing into central territory while securing the northern and eastern neighbourhoods. By June they had encircled Zinjibar and were closing in on the city, culminating in its complete liberation on 12 June.

The seizure of Zinjibar concerned the United States, which provided support for Yemeni ground forces and launched airstrikes on militants during the battle alongside Saudi Arabia. Between 500 to 1,000 soldiers were estimated to have died in the battle along with at least 600 militants. During their occupation, Ansar al-Sharia administered Zinjibar under Sharia and provided basic services for civilians. Most of the city's near 20,000 residents fled to neighbouring governorates leading to a refugee crisis. Destruction was widespread, and both sides were accused of human rights violations by Amnesty International and Human Rights Watch.

The participation of tribal forces (officially organized into the Popular Committees) was considered crucial to the government's victory. Zinjibar's strategic position near Aden may have pushed the government to send additional forces to Zinjibar to prevent the expansion of Ansar al-Sharia's territory. In the context of the revolution, the opposition accused President Ali Abdullah Saleh of undermining military forces in Zinjibar or having intentionally let the city fall in order to display his leadership as indispensable for Yemen's security, although this has been disputed.

Background As part of the wider Arab Spring, protests in Yemen began demanding the ouster of longtime president Ali Abdullah Saleh in 2011, sparking the Yemeni revolution. The upheaval escalated after security forces fired upon a crowd of demonstrators on 18 March, killing dozens. Influential general Ali Mohsen al-Ahmar and other military officers announced their defection to the opposition afterwards. The "highly personalistic" Yemeni Armed Forces proceeded to split between factions siding with Ahmar and the revolution and those loyal to Saleh. The government's control of the southern parts of Yemen was already limited prior to the revolution and broke down further as the political conflict grew more intense, with figures from both pro and anti-regime factions drawing security units deployed in the south to areas around the capital where the crisis was centered.

Formed in 2009, al-Qaeda in the Arabian Peninsula (AQAP) was primarily concerned with organizing terrorist attacks on the United States prior to the revolution, while keeping a low profile in Yemen. The group began to shift towards an insurgency against the Yemeni government in June 2010. In August, it took over the town of Lawdar in Abyan Governorate, sparking a brief battle which ended in their withdrawal. Another round of urban combat occurred the following month in al-Hawtah, a village in Shabwah Governorate. These engagements among others allowed AQAP to amass experience in armed combat with security forces.

The southern governorates of Abyan and Shabwah had been historical AQAP hideouts for their mountainous terrain and independent tribes. Unlike other al-Qaeda affiliates, AQAP never held or administered territory in Yemen until 2011. When asking Osama bin Laden months before the start of the Arab Spring, AQAP leader Nasir al-Wuhayshi was told his group did not have enough popular support to establish an outward presence. But with the regime's preoccupation with its own survival and fractures within the military, AQAP leadership believed there to be an opportunity to gain a foothold in Yemen. With increased freedom for operations after the 18 March massacre, militant forces quickly captured the town of Jaar in Abyan on 27 March after security forces fled the area. Preoccupied with the revolution, the government paid little concern. Senior AQAP cleric Adel al-Abab said in an April interview that AQAP was controlling Jaar under the name Ansar al-Sharia and would soon target the nearby provincial capital of Zinjibar.

Combatants

Ansar al-Sharia

The militants controlling Zinjibar referred to themselves as Ansar al-Sharia. Despite the nominal difference, Ansar al-Sharia was widely believed to be affiliated with or a direct extension of AQAP. A month prior to the battle, Abab identified Ansar al-Sharia as "what we use to introduce ourselves in areas where we work to tell people about our work and goals, and that we are on the path of Allah". Ansar al-Sharia declared Jalal Baleedi (Abu Hamza) as the emir of Zinjibar, but were formally led by Wuhayshi, the leader of AQAP. Said Ali al-Shihri and Qasim al-Raymi, the deputy leader and military commander of AQAP respectively, were the primary planners of the takeover of Zinjibar and other towns in the south.

Around 700 to 1,000 mitalints were estimated to be in Zinjibar by the end of 2011. Most were Yemenis from the local populace and other areas of the country, while there were also small numbers of foreign fighters from other Arab and non-Arab states. Some foreigners had joined after arriving from Aden International Airport pretending to be tourists. The militants dressed in traditional fouta robes, and many were noted for their long hair and large beards. Fighters were fitted with canvas military vests loaded with ammunition, grenades, and a copy of the Quran.

Ansar al-Sharia forces were well-equipped and possessed heavy weaponry, most of which was seized from security forces during the initial stages of the battle. This included heavy artillery, anti-aircraft weapons, tanks, and armored transports. At least two stolen T-62 tanks were operated by the militants, but their effectiveness was negligible before they were disabled by airstrikes. Other weaponry utilized by the militants included mortars, snipers, machine guns, rocket-propelled grenades, Strela anti-air launchers, machine gun technicals, and Katyusha rocket artillery. Fighters on the ground were described as being disciplined, highly organized, and having a clear strategy, operating in small cells while utilizing knowledge of the area.

Yemeni government The seven conventional brigades that fought in Zinjibar were mostly armored or mechanized units and belonged to the Southern Military Region command of the Yemeni Land Forces. Three units were involved in most of the fighting; the 25th Mechanized Brigade, along with the 119th Infantry Brigade and 201st Mechanized Brigade. These brigades were estimated to comprise 1,000 soldiers each, though the 25th Mechanized Brigade had also been numbered at around 2,000 soldiers. Three other brigades were later deployed during August, them being the 31st Armored Brigade, 39th Armored Brigade and 115th Infantry Brigade. The 135th Infantry Brigade joined the fight in April 2012. The full strength of Yemeni forces in Zinjibar was numbered at 10,000 troops by the end stages of the battle.

Military units aligned with different sides of the revolution fought alongside each other during the battle. The 25th Mechanized Brigade, despite having connections to Ahmar, remained neutral and coordinated with units of both orientations. Meanwhile, units such as the 119th Infantry Brigade and 135th Infantry Brigade supported Ahmar and the revolution, while the 31st Armored Brigade and 201st Mechanized Brigade were loyal to Saleh.

During the months-long siege on the 25th Mechanized Brigade's base they were surviving mainly off rice and well water; journalist Jeremy Scahill, who toured the frontlines of Zinjibar with brigade personnel, described them as "thin and haggard, many with long beards and tattered uniforms or no uniforms at all." Soldiers were not required to wear body armour due to the intense heat of the region. The brigade's inexperience in guerilla warfare and shortage in equipment such as night-vision goggles and snipers, and the government's inadequate deployment of special forces in the city, hampered its ability to effectively fight the militants during 2011. Associated Press described military forces in Abyan at large as "ill-equipped, poorly trained with weak intelligence capabilities" and "riven with conflicted loyalties".

The Central Security Forces (CFS) and elite Counter-Terrorism Unit (CTU), both components of the Ministry of Interior rather than the military, were officially deployed in Zinjibar to support the army in early April 2012, though a journalist from Le Monde had written of a CTU force of 120 soldiers fighting on the frontlines since November 2011. According to a CTU officer in Abyan, the unit was directly coordinating with conventional army forces on the ground and "participates in battles but in tactical ways." The Republican Guard was also called in by June 2012.

Battle Ansar al-Sharia takeover (May 2011) On 27 May, around 300 fighters from Ansar al-Sharia departed from Jaar and, after a travelling through a stretch of mountains, descended into Zinjibar unopposed. Attributed to an "intelligence breakdown", the surprise invasion was completed within a few hours and without any response by government forces stationed in the city. The first target of the militants was the local base of the Central Security Forces (CSF) on the eastern outskirts of the city. It was quickly abandoned by its soldiers, allowing for the militants to raid it and loot the equipment. Most of the CSF fled to the headquarters of the 25th Mechanized Brigade on the southeast edge of the city. After equipping themselves with the looted weapons, Ansar al-Sharia proceeded to besiege the base while other militants spread through the city and captured it uncontested, including the local government headquarters.All government buildings were taken over, while surrendering soldiers were reportedly executed and occupants of the main prison were released.