The remains of at least 400 people have been discovered near an Iraqi town which has just been retaken from Isis, an official has said.

The mass graves were found at an airbase on the outskirts of Hawija, a town occupied by the militants until early last month. It had been under Isis’ control since 2013.

Bodies wearing civilian clothes, fatigues and the orange jumpsuits Isis makes prisoners wear were among the dead, Kirkuk province governor Rakan Said told media. He did not say when the authorities would begin exhuming the bodies.

Isis kills 128 civilians in 'revenge' surprise counter attack on Syrian town

Local shepherd Khalaf Luhaibi who helped the security forces find the site told AFP that Isis brought prisoners to the area and shot them or poured oil over them and set them on fire.

More than 72 such sites have been discovered as US-backed forces across Iraq and Syria have succeeded in the full-scale fight to drive Isis out of its territory over the last year. It is estimated the graves could contain between 5,200 -15,000 people in total.

More than 95 per cent of Isis’ so-called caliphate has been reclaimed from the group, although advancing Iraqi coalition and Syrian Democratic Forces (SDF) troops face pockets of resistance.

In pictures: Isis' weapons factories Show all 11 1 /11 In pictures: Isis' weapons factories In pictures: Isis' weapons factories A mortar round fin manufactured by Isis in Gogjali, Mosul, November 2016 Conflict Armament Research In pictures: Isis' weapons factories Isis rocket components discovered in Gogjali, Mosul, Iraq in November 2016 Conflict Armament Research In pictures: Isis' weapons factories Isis mortars discovered near Karamlais, Iraq, in November 2016 CAR In pictures: Isis' weapons factories An Isis rocket launch frame in Qaraqosh, November 2016 Conflict Armament Research In pictures: Isis' weapons factories A memo from Isis' COSQC on quality control at a manufacturing facility in Gogjali, Mosul, November 2016 Conflict Armament Research In pictures: Isis' weapons factories Electrically-operated initiators manufactured by Isis in forces Gogjali, Mosul, November 2016 Conflict Armament Research In pictures: Isis' weapons factories Isis mortar tubes at a manufacturing facility in Karamlais, November 2016 Conflict Armament Research In pictures: Isis' weapons factories An Isis mortar production facility discovered in Gogjali, Mosul, in November 2016 Conflict Armament Research In pictures: Isis' weapons factories An Isis weapons manufacturing facilities near Mosul in November 2016 Conflict Armament Research In pictures: Isis' weapons factories Stocks of French-manufactured Sorbitol, Latvian potassium nitrate and Lebanese sugar at an Isis weapons factory in Iraq Conflict Armament Research In pictures: Isis' weapons factories A destroyed Isis weapons facility in Qaraqosh, Iraq, November 2016 Conflict Armament Research

There is still fierce fighting in the desert border region. Isis has also managed to recapture more than half of the Syrian town of al Bukamal, two days after the Syrian army declared it freed of militants.

The last town under Isis control in Iraq is Rawa, which came under attack by Iraqi forces over the weekend.