Iraq carried out air strikes Tuesday against jihadists who have for months besieged the town of Amerli, where residents are short on food and water and face a "possible massacre."

The nine strikes by Iraqi warplanes targeted forces from the Islamic State (IS) jihadist group, Colonel Mustafa al-Bayati said.

IS spearheaded a major offensive in June that overran large areas of Iraq and cut off the Shiite Turkmen-majority town.

Time is running out for its residents, who are in major danger both because of their faith, which jihadists consider to be heresy, and their resistance against the fighters, which has drawn deadly retribution elsewhere.

"The people are still besieged and stranded there," said Eliana Nabaa, the spokeswoman for the UN mission in Iraq.

There is "no possibility of evacuating them so far," and only limited humanitarian assistance is reaching the town, she said.

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

Nihad al-Bayati, who worked as an engineer at the Tikrit oil refinery but is now fighting to protect his hometown, said its defenders, who are made up of police and volunteers, have repelled two attacks in recent days.

Residents face a major shortage of both food and water, there is no electricity, and the helicopter flights delivering aid and ammunition are targeted with machinegun fire on the way in, and mortar rounds once they land, Bayati said.

"The pilots are suicidal," he said, but the aircraft have been able to land and depart so far.