Hundreds of families have been abducted by ISIS from their town near Mosul in Iraq, the UN human rights organisation said today, warning that they may be used as human shields during the battle to retake the city.

Spokeswoman for the UN high commissioner for human rights, Ranina Shamdasani, said that 1,500 families were last week forced to retreat from Hammam al-Alil, which lies to the south of Mosul.

Almost 300 former Iraqi soldiers were also taken, Shamdasani said today at a UN briefing.

"People forcibly moved or abducted, it appears, are either intended to be used as human shields or – depending on their perceived affiliations – killed," she added.

"The fate of these civilians is unknown for the moment."

The abducted families were being taken from their town to Mosul airport, Shamdasani said.

About 100 of the former Iraqi Security Forces officers were taken at around midnight on November 3 from Mawaly village, which is about 20 km (12 miles) west of Mosul. A further 195 were abducted between November 1 and November 4 from villages in Tal Afar district.

The UN also had information that at least 30 sheikhs were abducted in Sinjar district on November 2 or November 3 and taken to an unknown location. It was trying to verify a report that 18 of them had been killed on November 4 in Tal Afar district, Shamdasani said.

The operation against Islamic State's Iraqi stronghold has entered its fourth week and Iraqi forces have so far gained just a small foothold in Mosul.

The UN human rights office has sources on the ground but the information they are able to provide is "patchy", Shamdasani said.

She could not confirm media reports of a mass grave being found but said it happened to be in the same agricultural college in Hammam al-Alil where the UN reported the execution of 50 police officers last month.

Additional reporting by Reuters.