Iraqi warplanes have begun targeting jihadists besieging the Shia Turkmen town of Amerli amid growing fears for the safety of thousands of residents short of food and water and facing a "massacre".
With some 12,000 Turkmen trapped in the northern town, US President Barack Obama is "nearing a decision" to authorise strikes and aid drops in the area, The New York Times reported.
The report added that Obama is also seeking to piece together an international coalition for potential military action in Syria, where the US has begun reconnaissance flights.
And nine countries have committed to providing arms to Iraq's Kurdish peshmerga forces, who are fighting in north and east Iraq against Islamic State jihadists leading a sweeping offensive that has overrun large areas of the country.
Iraqi warplanes carried out nine air strikes on Tuesday against the militants besieging Amerli, an officer said.
Helicopters delivering aid and ammunition to the area are targeted with machinegun fire on the way in, and mortar rounds once they land, said Nihad al-Bayati, who worked as an engineer at the Tikrit oil refinery but is now fighting to protect his hometown.
"The pilots are suicidal," he said, but the aircraft have been able to land and depart so far.
Time is running out for Amerli's residents, who face danger both because of their Shia faith, which jihadists consider heresy, and their resistance against the jihadists, which has drawn deadly retribution elsewhere.
There is "no possibility of evacuating them so far", and only limited humanitarian assistance is reaching the town, said Eliana Nabaa, the spokeswoman for the UN mission in Iraq.
UN Iraq envoy Nickolay Mladenov has called for an urgent effort to help Amerli, saying residents who have been under siege for more than two months face a "possible massacre" if it is overrun.
Residents are suffering from a major shortage of both food and water and there is no electricity, said Bayati.
US officials warn that the Turkmen are facing the same dangers as those faced by thousands of Iraqi Yazidis, who were driven to Mount Sinjar after attacks by the militants, many of them dying of thirst and starvation.
Countries are lining up to arm Iraqi Kurdish forces, which were pushed back by jihadists toward their regional capital Arbil earlier this month but have clawed back ground with the help of US strikes and international assistance.
Pentagon chief Chuck Hagel put the number of countries on board at eight, while Kurdish regional president Massud Barzani said that Iran has provided arms and equipment as well, bringing the total to at least nine.
The United States has meanwhile launched reconnaissance flights of IS positions in Syria, multiple sources said, in surveillance seen as a precursor to possible US strikes that would greatly expand its conflict against IS.
The US focus on Syria comes after President Bashar al-Assad's regime said on Monday it was willing to work with the international community, including Washington, to tackle extremist fighters.
But American officials said they did not plan to coordinate with Damascus on targeting IS militants in Syria, despite Syrian insistence that any military action on its soil must be discussed in advance.
International concern about IS has been rising after a lightning offensive by the group through parts of Iraq and a string of brutal abuses, including the murder of US journalist James Foley.
The US began air raids against IS in Iraq on August 8, in a bid to roll back its advances. It said that two air strikes near Arbil on Tuesday destroyed two IS armed vehicles and damaged another.
But US Chairman of the Joint Chiefs of Staff General Martin Dempsey has acknowledged that the group cannot be defeated "without addressing that part of the organisation that resides in Syria".