The United States is weighing a possible humanitarian mission as well as air strikes to help Shiite Turkmen encircled by Islamic State jihadists in northern Iraq, US officials said Wednesday.

If approved, the operation in Amerli could resemble US military action taken earlier this month to aid thousands of vulnerable Yazidis at Mount Sinjar, also in Iraq's north, officials said.

In that case, American cargo aircraft dropped food and water to the Yazidis while warplanes bombed Islamic State (IS) militants nearby.

A US defense official said "no final decision has been taken" and said the administration was still trying to gain a clear picture of events in the northern town.

"We're still in a fact-analysis situation," said the defense official, who spoke on condition of anonymity.

UN officials have warned of growing shortages of food and water in Amerli and that the Shiite Turkmen face a "possible massacre" if the town is overrun by Islamic State fighters.

As Washington looked at potential intervention, Iraqi security forces and Shiite militia massed to the north and south of Amerli to break the siege of the town that has lasted more than two months.

A second US defense official said different scenarios were being considered by Washington, depending on what was required and what Baghdad requested.

"It could be a humanitarian operation. It could be a military operation. It could be both," the defense official, who also asked not to be named, told AFP.

A Pentagon spokesman acknowledged that Washington was watching events in Amerli "closely."

"I won't get ahead of operations or missions that we aren't conducting yet but we are certainly mindful of the fact that... there is more human suffering in Iraq," Rear Admiral John Kirby told CNN when asked about Amerli.

"One of the reasons we do conduct some kinetic activity, some air strikes inside Iraq, is to assist with humanitarian efforts."

Amid fears of a mounting crisis in Amerli, General Lloyd Austin, head of US Central Command, who oversees American forces in the Middle East, held talks in Baghdad on Wednesday with this Iraqi counterparts, officials said.

State Department spokeswoman Jen Psaki told reporters the United States was working to build an international coalition to tackle the threat posed by IS jihadists.

"This is an effort that is going to require significant focus and all hands on deck -- not just the United States, but a range of countries," she said.