PARIS - Relatives of French jihadists and their families held in Syria say the Turkish offensive and the ensuing advance of Syrian President Bashar al-Assad's forces have added to the urgency of bringing them home.

Hundreds of radicalized French men and women traveled to Syria to join IS at the peak of the group's dominance, sometimes taking their children with them.

Most were captured when the extremist group was militarily defeated by Kurdish-led forces, backed by an international coalition.

Around 12,000 IS fighters, including 2,500-3,000 foreigners, are being held in Kurdish prisons with a further 12,000 foreigners - 8,000 children and 4,000 women - detained in camps in northeast Syria, according to Kurdish sources.

Turkey is now taking control of parts of the area as it presses its operation against Syrian Kurdish fighters. At the same time Assad's forces are advancing from the south to contain the Turkish offensive.

Referring to the fate of the jihadists, Asma, a French woman whose brother is being held in a Syrian Kurdish prison, asked: "If Bashar al-Assad retakes the prisons, what is going to be their future?"

"Either they will be tortured or they will be used for bargaining or they are going to escape," said Asma, who like other sources interviewed by AFP for this story asked for her name to be changed.

The worst scenario, she said, would see them end up back in the hands of Islamic State, allowing "a terrorist organization to be rebuilt."

The fate of the foreign fighters and their relatives has divided the Turks and their Syrian Kurdish foes, with both sides accusing each other of freeing prisoners in a bid to sow chaos.

"I'm hoping for just one thing - that the state repatriates them," said another woman Estelle, who believes a male relative is being held in Derik prison in Syria.

"If Bashar al-Assad's regime retakes the prisons I do not know if it will be possible to go and find him," she said.