Oulfa Hamrounni reads the Koran with daughters Taysin and Aya. Her older daughters, Rahma and Ghofran, are held by a Libyan militia, which captured them after they had joined the Islamic State and married fighters who were later killed. (Lorenzo Tugnoli/For The Washington Post)

In a small box in her bedroom, Oulfa Hamrounni keeps the photo she treasures most. It shows one of her daughters, brown hair flowing, a smile on her round face. The photo was taken before the girl and her sister left home to join the Islamic State’s affiliate in Libya.

Today, Hamrounni is struggling to bring her teenage daughters back to Tunisia. She’s also trying to prevent two others from joining them.

“I am afraid for my younger daughters,” she said. “They still have the same ideology of my older daughters.”

The younger ones are 11 and 13.

Hundreds of foreign female Islamist militants, including many Westerners, have journeyed to the battlegrounds of Syria and Iraq to begin new lives under the Islamic State, also known as ISIS or ISIL. Now, there are signs that they are being encouraged to travel to Libya as well, signifying a shift in the strategy of the terrorist network as it faces growing threats and constraints to its operations in the Middle East.

Before she and her sister became radicalized, Rahma played the guitar. She and Ghofran often wore T-shirts and mingled with boys in cafes, and neither wore headscarves, their mother said. (Lorenzo Tugnoli/For The Washington Post)

Most radicalized women and girls join the Islamic State to marry fighters and bear their children, which helps the group’s arm in Libya build a state, mirroring the strategy in Syria, experts who monitor jihadist activity have said. The creation of family structures deepens the Islamic State’s reach and ideology in its territory, which makes it more difficult for Western and regional governments to eradicate the militants and defuse their threat in North Africa.

“Official propaganda showcases Libya as the new frontier of the self-proclaimed caliphate,” said Melanie Smith, a researcher with the London-based Institute for Strategic Dialogue, which focuses on violent extremism. “Hence the encouragement of foreign females signifies a need to consolidate the land they have managed to acquire.”

When he announced the “caliphate” in 2014, Islamic State leader Abu Bakr al-Baghdadi specifically invited women alongside male engineers, doctors, lawyers and architects, signifying that the women’s “primary responsibility is to physically build and populate territory,” Smith said. As wives, their role is to be dutiful and obedient to their militant husbands. As mothers, they nurture the next generation of fighters. Some women also have combat duties.

Rahma, 17, became the wife of Noureddine Chouchane, a senior Tunisian Islamic State commander thought to have been killed in a U.S. airstrike on the Libyan city of Sabratha on Feb 19. Her 18-year-old sister, Ghofran, was married to an Islamic State militant who was killed after the attack. Six months ago, she gave birth.

Both sisters are now in the custody of an anti-Islamic State militia in Tripoli, the Libyan capital.

On a recent day, their mother sat in her small rented house in Mornag, a gritty town 15 miles south of Tunis. In front of her was the photo of Rahma.

“They used to be the opposite of this,” she said in a low, resigned voice.

From T-shirts to niqabs

The sisters loved hard-rock music.

Rahma played the guitar. She and Ghofran often wore T-shirts and mingled with boys in cafes. They eschewed the headscarves favored by many Muslim women, their mother said.

But their family life was troubled. Their father struggled to find work and often came home drunk, Hamrounni said. In 2011, the couple divorced, and he disappeared.

By then, Tunisia was in the midst of its Arab Spring revolution. With the toppling of dictator Zine ­el-Abidine Ben Ali and the new openness that followed, religious extremists made inroads with disaffected youths frustrated by the lack of jobs and opportunities. One group set up an Islamic education camp across the street from Hamrounni’s home in the central city of Sousse.

From a loudspeaker, the imam implored young people to give up their Western influences, warning of catastrophic consequences.

First Ghofran joined the camp, then Rahma.

“I was happy that my daughters were respecting Islam,” Hamrounni recalled.

They began wearing the niqab — a black veil with an opening for the eyes. They stopped watching television, save for religious programs. They avoided shaking hands with males. They urged their two younger sisters to leave school because it was secular and taught by “nonbelievers.”

One day, Rahma threw her guitar and CDs into the trash. Western music was now taboo. On another day, the sisters tossed out their hard-rock T-shirts. They burned pictures of themselves playing music, the ones with their faces uncovered.

All except the photo their mother keeps in her box.

‘By then, I had lost control’

More than 700 Tunisian women have joined the Islamic State and other militant groups in Syria and Iraq, according to the nation’s Ministry of Women. Badra Gaaloul, a researcher with the Tunis-based International Center of Strategic, Security and Military Studies, estimates that there are more than 1,000 female foreign Islamist militants in Libya, including 300 Tunisians. Others are from Sudan, Syria, Egypt and Morocco, as well as Western European nations.

“They serve as wives, mothers, as religious instructors to teach the laws of the Islamic State,” Gaaloul said. “They also police areas and train to be fighters and suicide bombers.”

Researchers are noticing efforts on social media to lure more female militants to the Libyan coastal city of Sirte, which the Islamic State seized in the chaos that has followed the death of Libyan dictator Moammar Gaddafi in October 2011. In tweets, monitored last fall by the Institute for Strategic Dialogue, female jihadists urged followers to head to Libya, noting that routes from Turkey into Syria were blocked.

“How many brothers & sisters rn in Turkey cannot go back home, and cannot enter in . . . Make your visa and go to #IS in #Libya,” wrote an extremist named “Zawjah Shahid,” Arabic for “martyr’s wife.”

By 2014, Rahma and Ghofran were attending ceremonies celebrating the martyrdom of Tunisian jihadists killed in Syria. Through social media and websites, they learned about the armed groups fighting there. They put black Islamic State flags in their bedrooms.

“By then, I had lost control of my daughters,” Hamrounni said.

They also began to radicalize their younger sisters, Taysin and Aya. They bought a toy Kalashnikov rifle and showed them how to operate it. They showed them videos of how the Islamic State trains children to use weapons.

“We used to watch how they taught children to become snipers,” said 11-year-old Taysin.

“They always told me to join ISIS and go into the field and fight,” said 13-year-old Aya.

In late 2014, Hamrounni crossed the border with her family to the Libyan city of Zawiyah to find work. The war’s violence had not reached there.

Within weeks, Ghofran had fled the house. Two days later, the family returned to Tunisia. Hamrounni restricted Rahma’s movements, but that didn’t stop her aspirations.

Last summer, she vanished, too.

‘We have to fight’

In Libya, while her sister was the dutiful wife of a militant, Rahma trained in weapons. Her mother thinks she was in Sabratha with other Tunisian extremists to launch an attack in the country. After the U.S. airstrike, the sisters were captured.

In a phone interview, Ahmed Omran, a spokesman for the Libyan militia, acknowledged that the girls were in its custody but declined to comment further.

Hamrounni has appeared on national television, chastising the Tunisian government for not doing more to get her daughters released, even though she is aware they would be thrown in jail. Tunisia’s Interior Ministry did not respond to calls and emails seeking comment.

Hamrounni no longer allows her two younger daughters to access Facebook. She doesn’t let them speak to their older sisters the rare times they call.

“I am not with the Islamic State now,” said Taysin, a precocious girl dressed in pink with a black headscarf.

But as the conversation flowed, it became apparent that she still felt some sympathy for the militants’ ideology.

“The nonbelievers, they have to be killed,” Taysin said. “The nonbelievers are trying to beat Islam. We have to fight them.”

Next to her, a doll lay on a shelf. Taysin had named her Rahma.

When asked how she felt about her older sisters joining the Islamic State in Libya, she answered, “They did the right thing.”