Syrian pro-government forces patrol in the eastern city of Deir Ezzor in November 2017
Beirut (AFP) - Syria's Deir Ezzor hosts a patchwork of rival forces and their international partners, from Russian-backed government troops and US-backed forces to Shiite militias and jihadists.
On Thursday, the US-led coalition said it killed at least 100 pro-regime fighters to fend off an attack on its own allies there.
With the myriad forces increasingly turning their guns on each other, AFP takes a look at their competing interests.
- Borders, oil, tribes -
Deir Ezzor is bordered by Syria's Raqa province to the north, Homs to the west, and Iraq to the east. The largely desertic governorate is bisected diagonally by the Euphrates River.
East of the river lie the Omar oil field, which had a pre-war output of 30,000 barrels per day, and the Conoco gas field, which produced 13 million cubic metres daily before 2011, according to The Syria Report.
Some of Syria's most influential tribes, including the Shaaytat and Busayra, are from Deir Ezzor.
- IS, cornered -
In 2014, the Islamic State group overran much of Deir Ezzor and the eponymous provincial capital.
But by late 2017, the jihadists were losing to two parallel offensives, one by Russian-backed regime forces and the other by a US-backed alliance.
Now, 800 IS fighters at most hold tiny pockets of Deir Ezzor province near the Iraqi border, according to the Syrian Observatory for Human Rights.
- Russia-backed regime -
With Russian air cover, forces loyal to Syrian President Bashar al-Assad fought a months-long offensive against IS in 2017.
Tens of thousands of pro-government fighters now control the western half of the province and parts of the eastern river bank.
They include thousands of tribal fighters, as well as Iraqi and Iranian forces based in Albu Kamal near the Iraqi border.
Shiite Afghan militiamen are stationed in the town of Mayadeen, while Lebanese movement Hezbollah is scattered across the province.
The regime's main interest in Deir Ezzor, says Washington-based analyst Hassan Hassan, is territorial.
"It's straightforward for the regime -- it wants to take all of Syria," said Hassan, a senior fellow at the Tahrir Institute.
To that end, it is building deep relationships with tribes to lay the groundwork for a comeback, he said.
- US-backed alliance -
East of the Euphrates are several thousand fighters from the Syrian Democratic Forces (SDF), an alliance of Kurdish and Arab forces.
With US-led bombing raids, the SDF ousted IS from Deir Ezzor's eastern half, including the Omar and Conoco fields.
The coalition's top priority in carving out this zone is securing the Iraqi border against a possible IS resurgence.
"The SDF and the Americans think they are best suited to fight IS and prevent IS from coming back. They don't think the regime is strong enough to do the job," said Hassan.
- Increasing friction -
In 2017, the US and Russia agreed to a "de-confliction line" along the Euphrates River to prevent the separate anti-IS offensives they were backing from clashing.
But the forces have still butted heads, with the SDF accusing Russia of bombing its forces multiple times.
In the latest incident, the US-led air alliance bombed pro-regime fighters attacking SDF and coalition forces, a US military official said Thursday.
Even if it can't mount a full-on offensive against the SDF, the regime is attacking its positions to demonstrate it still has a role to play, said Hassan.
"The regime understands that any day that goes by with the Americans building something there, that makes it that much harder for it to go back to these areas," he said.
In the foreseeable future, the coalition will likely dig in its heels to protect the area from further regime attack, while opting to reinforce the de-confliction line over escalating, Hassan said.