She and her two sisters were among thousands of women and girls from the Kurdish-speaking Yazidi minority taken hostage by IS as it swept into Iraq's Sinjar region in August 2014.

"But it will be full of revenge until all the women are freed."

"When I started fighting, I lifted some of the worries from my heart," she says, surrounded by fellow Yazidi militia women in Raqa's eastern Al-Meshleb district.

Her hair tucked under a tightly wrapped forest green shawl embroidered with flowers, Heza says battling IS in its Syrian bastion has helped relieve some of her trauma.

She was trafficked into Raqa as a sex slave by the Islamic State group but managed to escape. Now Yazidi fighter Heza is back to avenge the horrors she and thousands of others suffered.

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The women were sold and traded across the jihadists' self-proclaimed "caliphate" in Syria and Iraq. Around 3,000 are believed to remain in captivity, including one of Heza's sisters.

"When the Yazidi genocide happened, Daesh snatched up the women and girls. I was one of them," Heza recounts, using the Arabic acronym for IS.

ensive by the Syrian Democratic Forces (SDF), an alliance of Kurdish and Arab fighters, to retake the city from Islamic State (IS) group fighters (photo by: BULENT KILIC/AFP)

The United Nations has qualified the massacres IS carried out against the Yazidis during the Sinja

r attack as genocide.

IS separated Yazidi females from the men in Sinjar, bringing the women and girls into Raqa.

"They took us like sheep. They chased us and humiliated us in these very streets," Heza tells AFP, gesturing to a row of heavily damaged homes in Al-Meshleb.

The eastern district was the first neighbourhood captured from IS by the US-backed Syrian Democratic Forces, a Kurdish-Arab alliance, in their months-long offensive to seize the jihadist bastion.

SDF officials told AFP that their forces had already rescued several female Yazidi captives, including a 10-year-old girl, since they entered Raqa city in June.

'Despite pain, I felt joy'

Over the course of her 10-month captivity in Raqa, Heza was bought by five different IS fighters.

Yazidi fighter Heza prepares her rifle in an abandoned home used as a base on the eastern outskirts of Raqa on July 18, 2017 (photo by: BULENT KILIC/AFP)

Her voice strained but her brown eyes still sharp, the young fighter says she prefers not to detail the abuses she suffered.

But in an indication of the extent of her trauma, Heza -- whose name means "strength" in Kurdish -- says she tried to commit suicide several times.

Finally, in May 2015, she escaped from the home where she was being held to a nearby market, and she found a Syrian Kurdish family who smuggled her out of the city.

She travelled around 400 kilometres (250 miles) across war-ravaged northeast Syria back into Iraq to join the Shengal Women's Units (YPS).

The YPS -- named after the Kurdish word for Sinjar -- is a part of the US-backed SDF.

Heza underwent intensive weapons training, and when the SDF announced its fight for Raqa in November 2016, she and other YPS fighters were ready.

"When the Raqa offensive began, I wanted to take part in it for all the Yazidi girls who were sold here in these streets," she says.

"My goal is to free them, to avenge them."

The SDF spent months tightening the noose around Raqa before breaking into the city in June, and the Y

PS took up their first positions in Al-Meshleb several weeks later.

It was the first time Heza was back in the northern Syrian city since her escape.

"When I entered Raqa, I had a strange, indescribable feeling. Despite the enormous pain that I carry, I felt joy," the fighter says.

'Revenge will be proportional'

s Units rests in an abandoned home used as a base on the eastern outskirts of Raqa on July 18, 2017 (photo by: BULENT KILIC/AFP)

Rifles are lined up in neat rows inside the abandoned home used by the YPS as their base in Al-Meshleb.

Yazidi women in brand-new uniforms gather around a crackling walkie-talkie for news from the front.

Some of them, like 20-year-old Merkan, have travelled far to join the fight against IS.

Her family is originally Yazidi Turkish, but Merkan and her 24-year-old sister Arin were raised in Germany.

When they heard about IS's infamous sweep into Sinjar in 2014, they were outraged.

"I could never have imagined a world like this. I didn't expect things like this could happen," Merkan says.

"I was in so much pain," says the tall militiawoman.

Her older sister decided to travel to Sinjar in late 2014 to join the YPS, and Merkan followed in early 2015.

"I only had one goal in front of me: liberating the Yazidi women, and all women who were still in Daesh's clutches."

She had scribbled a similar pledge in Kurdish on a wall behind her.

"Through strength and struggle, we Yazidi women fighters came to Raqa to take revenge for the August 3 massacre," the graffiti says, referring to when IS entered Sinjar.

"We are avenging Yazidi girls," it adds.

"Yesterday there was Al-Qaeda and today there's Daesh. We don't know who will come next. I want to go anywhere there is injustice," Merkan said.

Fellow fighter Basih is sitting quietly in a neighbouring room, chain-smoking cigarettes in the muggy July afternoon.

"We suffered the ugliest forms of injustice. Our revenge will be proportional to it," she

said