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.
Helicopters delivering aid and ammunition to the area are targeted with machinegun fire on the way in, and mortar rounds once they land, Colonel Mustafa al-Bayati said.
More From This Section
"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 Shiite 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.
Residents are suffering from a major shortage of both food and water and there is no electricity, said Nihad al-Bayati, who worked as an engineer at the Tikrit oil refinery but is now fighting to protect his hometown.
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.