Rebels, Christian militiamen, local fighters: a cluster of Syrian Arabs united by their hatred for the Islamic State group have cast their lot with Kurdish forces to defeat the jihadists.
But the choice is a controversial one, as Syria's mainstream armed opposition has branded them traitors for foregoing the fight against the regime in Damascus to wage war on the jihadists.
Formed in October 2015, the US-backed Syrian Democratic Forces (SDF) have dealt blows to IS across swathes of territory in the north of the war-torn country.
The 25,000-strong force is dominated by the powerful Kurdish People's Protection Units (YPG) but the Arab contingent has been steadily growing to around 5,000 fighters.
The alliance comprises 25 Arab factions, three Kurdish ones, one group of Syriac Christian fighters as well as two Turkmen factions.
Many were rooted in the rebel movement that rose against President Bashar al-Assad but which has become largely gutted after the rise to power of hardliners and jihadists groups like IS.
Arab SDF members say their alliance stands out as the most efficient amid the disjointed chaos of other opposition groups.
"We allied ourselves with the Kurds because they are the most organised and have the most weapons and money," Yasser al-Kadro, a military commander in the Raqa Falcons Brigade, told AFP.
The 1,000-strong brigade is a key Arab component of the SDF, and its fighters all hail from Raqa, the northern border province that has served as IS's bastion since 2014.
These fighters believe the SDF is their best chance at kicking IS out of Raqa.
- No other choice -
"In Raqa, there is either IS or the YPG -- so we allied ourselves with the YPG to fight IS," Abu Saleh, Raqa Falcons Brigade's top military commander, told AFP.
"If we had found a united Syrian faction that brought together all Syrians, we would have joined it."
The same applies to fighters around Manbij, a key transit town on IS's supply route from the Turkish border.
Ali Hajjo deserted from the government's police force and now heads the Euphrates Brigades, one of the main factions encircling IS-held Manbij.
He said local fighters joined the SDF because it was by far "the most organised group" and the best shot they had to recapture their towns.
A journalist working with AFP who toured several SDF positions said even when Arab units were engaged in battle, senior Kurdish field officers are present to monitor developments.
The SDF receives air support from the US-led coalition, while more than 200 US special operations forces advise them on the ground.
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According to the US, Arab fighters make up the majority of the SDF's operation around Manbij.
The SDF has even appealed to Christian fighters.
The Syriac Military Council was formed in the northeastern Hasakeh province in 2013, but recently merged its 500 fighters with the SDF.
Its spokesman, Kino Ghibrael, said his group aims to "protect the Syriac presence in the region" from IS.
- 'Betrayed the uprising' -
While its primary focus is to battle IS, the SDF has also been active in Aleppo province where it seized territory from an alliance of rebel groups led by Al-Qaeda's Syria affiliate, Al-Nusra Front.
The Army of Revolutionaries (Jaish al-Thuwwar) fought alongside the SDF to seize the key Minnigh airport and expel Al-Nusra and allied rebels from a series of towns north of Aleppo city.
Its head, Ahmad al-Omar, told AFP he decided to align himself with the SDF to confront "Islamist factions on the ground".
Al-Nusra, a rival of IS, kicked Jaish al-Thuwwar out of their home province of Idlib in 2014 and Omar says his goal now is to drive them out.
The predominance of YPG fighters in the SDF alliance has sparked concerns in Turkey.
Ankara regards the YPG as a branch of the rebel Kurdistan Worker's Party (PKK), which has waged a three-decade insurgency against the Turkish army.
And by opting to fight jihadists instead of the regime, the SDF's Arab fighters have also faced fierce criticism from Syria's mainstream opposition.
"The regime warplanes don't bomb them at all. This is enough to call them traitors," said Ali Jawad, 23, from Aleppo's Nureddin Zinki Islamist group.
"Anyone who joins the SDF or fights alongside them must be called out for betraying the uprising."
The regime is also suspicious of the SDF but considers that since they have a "de facto alliance" with the group since both sides are fighting the jihadists, according to a high-ranking military source.
"The Syrian government does not want to open any new fronts. The priority is to fight terrorism," the source told AFP.
The SDF is also treading a fine line in its ties with the regime.
Spokesman Talal Sello, a Turkman, said the SDF would not attack government forces, but also insisted it would be "impossible" for the group to fight alongside loyalist troops.