Islamic State (Isis) militants have kidnapped more than 900 Kurdish civilians in retaliation for the Manbij offensive forcing many into slave labour and some to fight for the extremists, say reports. The abducted civilians are said to have been forced into digging fortifications including bunkers and trenches whilst sending some boys, as young as 12, to fight on the front lines wearing Daesh (Isis) uniforms.

The claims have been made by a spokesman representing the 30,000-strong US-backed Syrian Democratic Forces (SDF) as they fight the jihadists in the northern part of the country. The Manbij operation, launched on 31 May, SDF and allied Manbij Military Council have recaptured much of the city with the help of US airstrikes.

Spokesman Sherfan Darwish said 26 of those abducted by IS have been murdered for refusing to follow orders from the jihadists after being kidnapped in the Aleppo countryside.

Once Syria's most populous city, Aleppo has been destroyed by five years of fierce battles and the Kurdish civilians on the edge of the city have been left vulnerable to raids. "Whenever Daesh is defeated, they retaliate against civilians," Darwish said, according to the Daily Mail.

The abductions have been taking place mostly in rural areas under IS control from western Manbij to the towns of al-Bab and al-Rai. Many of the civilians are being held in a prison in Qabasin digging fortifications underneath homes according to Kurdish media activist Rezan Hiddo.

The battle for Manbij has seen the SDF lose 89 fighters but reportedly kill 463 IS militants in the process. Among the IS militants killed was the governor of the besieged city, Osama al-Tounsi, by SDF shelling.

Also discovered in the city was a desert mansion believed to have belonged to IS leader Abu Bakr al-Baghdadi found abandoned. The discovery of the sprawling compound, complete with swimming pool and zoo, was discovered by Kurdish People's Protection Units (YPG).

It is feared that IS will use human shields to defend their territory as Kurds and Arab fighters begin an offensive all across northern Syria. "They are using the civilians as a cover. So you'll find them in the same building. In a civilian building, you'll find two or three apartments for IS fighters," said Abdel Aziz al-Hamza, a co-founder of the Raqqa is Being Slaughtered Silently group.

Manbij offensive
Fighters of the Syria Democratic Forces (SDF) stand inside a building near Manbij, in Aleppo Governorate, Syria, June 17, 2016.REUTERS/Rodi Said