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Ever since its defeat and withdrawal from its self-declared capital of Raqqa in October 2017, remnants of the Islamic State militant group have retreated deeper into eastern Syria.

However, while its Draconian rule over major cities in Syria and Iraq has come to an end, the militant group has retained control over pockets of territory on the eastern bank of the Euphrates river and in the desert close to the border with Iraq.

One of its last stands in this area is being made in the town of Hajin and its surroundings, where heavy clashes between IS fighters and the US-backed Syrian Democratic Forces (SDF) have been going on for weeks. The SDF launched the battle to retake the area on September 10.

In late November, IS launched a major counter-attack, killing 92 SDF fighters, according to the UK-based Syrian Observatory for Human Rights. It also reported that 61 IS fighters and 51 civilians died during the clashes.

Rami Abdel Rahman, the head of the Observatory, said the assault resulted in "the largest number of SDF fighters killed (by IS) in a single battle since it was founded". Both sides have suffered hundreds of casualties since September. The Observatory that more than 15,000 fighters supporting the anti-IS offensive arrived in eastern Syria in late November.

IS has been able to mount a fierce defence for a variety of reasons, observers say.

"The most important reason why the battle for the Hajin pocket has been so difficult is that IS has gathered a sizable cadre of its most committed fighters there," Nicholas A Heras, Middle East Security fellow at the Center for a New American Security, tells °®Âþµº.

"They have nowhere else to go."

Some reports have suggested that top IS leaders are based in the area.

Many of the IS fighters in Hajin fought during the long battle over Raqqa and were evacuated to eastern Syria’s Deir az-Zour province as part of a deal with the SDF and the coalition, says an anonymous military analyst known as Twitter user , who is closely following events in Syria.

IS had more than six months "to prepare their defence, digging many tunnels and underground caches". On the front lines, he says, there was no big difference between the weapons used by the SDF and IS.

IS is literally in a no-surrender, no-retreat mode, and that makes them fight harder and better

Another aspect that has helped IS' defence, says Heras, is that the militant group has "quite effectively" used the natural moat offered by the Euphrates river. The SDF has been unable to cross the river into regime-held territory to surround IS in Hajin.

IS in the Hajin pocket "is literally in a no-surrender, no-retreat mode, and that makes them fight harder and better than they might otherwise choose if there was a pathway for retreat open to them," says Heras.

Civilians stuck between the frontlines 

Civilians meanwhile remain trapped in the middle of the fighting. Various reports have highlighted civilian casualties as a result of the intensified violence in eastern Syria, including deaths caused by US-led coalition airstrikes.

Airwars, a monitoring group, cited local reports stating that coalition air and artillery strikes caused "significant civilian harm" in Deir az-Zour province between November 12 and 24. One of these occurred in the Hajin area, according to Free Deir Ezzor Radio, with dozens of civilians reportedly killed and wounded.

Overall, Airwars reported between 118 and 225 civilians were reported to have been killed during this two-week time period. Exact numbers are hard to come by, let alone confirm, in IS-held areas.

The US-led coalition has reported a steady stream of airstrikes in the Hajin area for weeks, but has warned that other sources have also carried out strikes in Hajin.

The UN at the end of October that at least 10,000 civilians were reportedly trapped in IS-held areas and around 27,000 displaced civilians were living in "dire conditions".

Commenting on Twitter last week, Omar Abu Layla, the head of the local Deir Ezzor 24 media organisation, said IS was ruling "with an iron fist" and civilians were under strict surveillance as IS was conducting extensive patrols. Some civilians were subjected to torture due to alleged violations, he commented.

The SDF has published of what it says are rescued civilians IS used as human shields in Hajin. The US-backed forces, made up of Kurdish and Arab fighters, also announced they had captured an IS security official formerly responsible for Deir az-Zour.

The way forward

The heavy battles over Hajin have also raised questions over US strategy in eastern Syria. The SDF has reportedly lost more than 450 fighters in the battle over Hajin since September alone. On December 3, IS launched further attacks against the SDF east of Hajin near the border with Iraq, Euphrates Post reported.

Heras, the security analyst, says there are two main options to speed up the Hajin campaign. The first involves "killing every last IS fighter in the Hajin pocket". In order to achieve this, the SDF needs a larger force "composed of local fighters from Deir az-Zour, and so far the SDF has had problems recruiting them". It would also require stepping up coalition airstrikes, which in turn would lead to higher civilian casualties, "including the local population stuck under IS rule and the families of IS members".

The second option is to offer the remaining IS fighters and their families a way to retreat into Iraq. This, Heras says, "might be smarter, but would upset Iraq, and the Assad government and its allies would seize on it and say that the Americans were letting IS live as an excuse to stay in Syria".

The most likely scenario is that the coalition and the SDF muddle through with the current slow-and-steady strategy

The US is concerned that developments elsewhere could distract from the mission to defeat IS. Last month the Pentagon announced it was setting up several observation posts in northern Syria to aid NATO ally Turkey secure its border.

Ankara has meanwhile been in conflict with the Kurdish-led People's Protection Units (YPG), a key component of the SDF, in northern Syria. Turkey believes the YPG to be the Syrian franchise of the Kurdistan Workers' Party (PKK), a militant group which has fought a bloody insurgency against Ankara for more than three decades. 

In reference to the battles in eastern Syria, US Secretary of Defence James Mattis : "What this is designed to do is make sure that the people we have fighting down in the [Middle Euphrates River Valley] are not drawn off that fight and that we can crush what's left of the geographic [IS] caliphate."

A third option may be available. "The most likely scenario is that the coalition and the SDF muddle through with the current slow-and-steady strategy, hoping that building attrition on the IS forces will lead to surrender," Heras concludes.

At the time of publication, SDF forces were pushing deeper into Hajin city, according to local reports.

Manuel Langendorf is a writer and editor focusing on the MENA region.

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