Iraqi security forces backed by volunteer militiamen on Thursday retook several villages located on the way to the town of Amerli, which jihadists have besieged for months, officers said.

Time is running out for Amerli's Shiite Turkmen-majority residents, who face danger both because of their faith, which jihadists consider heresy, and their resistance against the militants, which has drawn deadly retribution elsewhere.

And the town, besieged since militants led by the Islamic State (IS) jihadist group launched a sweeping offensive in June, is without electricity and running dangerously short on both food and water.

Army Staff Lieutenant General Abdulamir al-Zaidi told AFP that villages north of Al-Adhaim were retaken as part of a major operation aimed at advancing toward Amerli.

Brigadier General Khalaf Jassem confirmed that the villages had been retaken, and like Zaidi put the toll for militants at more than two dozen dead.

Senior Iraqi officials and officers frequently report large militant death tolls, but they are usually impossible to independently confirm.

In addition to the Iraqi forces advancing toward Amerli from the south, a civilian volunteer commander said that thousands of Shiite militiamen from groups including Asaib Ahl al-Haq and the Badr Organisation were gathering in the Tuz Khurmatu area, north of Amerli, in preparation for a battle to break the siege.

But reliance on such groups carries risks, especially after 70 people were gunned down in a Sunni mosque on August 22 by suspected Shiite militiamen.

Officials say that Washington is weighing both aid drops and air strikes to help the town.

"It could be a humanitarian operation. It could be a military operation. It could be both," a US defence official said on condition of anonymity.

And Iraqi aircraft are already carrying out strikes targeting the militants.

There is "no possibility of evacuating them so far", Eliana Nabaa, spokeswoman for the UN mission in Iraq, said of Amerli residents.

UN Iraq envoy Nickolay Mladenov has called for an urgent effort to help Amerli, saying residents face a "possible massacre" if the town is overrun.