The UN Security Council called an emergency meeting Thursday on the crisis sparked by the advance of Islamic State fighters who seized Iraq's largest Christian town, driving tens of thousands from their homes.

French President Francois Hollande offered to support forces combating the fighters during talks with Kurdish leader Massud Barzani and Pope Francis called on the world to protect the Christian minorities of northern Iraq after the fall of Qaraqosh.

And US President Barack Obama is expected to "imminently" decide on possible airstrikes or airdrops of food and medicine for tens of thousands of religious minorities dying of heat and thirst while fleeing IS forces, an administration official told The New York Times.

At UN headquarters in New York, France requested the urgent talks set to begin at 5:30 pm (2130 GMT).

"France is very deeply concerned by the latest advances in the north of Iraq and the taking of Qaraqosh, the biggest Christian city in Iraq, as well as by the intolerable abuses that were committed," French Foreign Minister Laurent Fabius said in a statement.

He urged world governments to "mobilize to counter the terrorist threat in Iraq and support and protect the population at risk."

The latest advance saw the Sunni extremist Islamic State extend its writ over northern Iraq and move within striking distance of semi-autonomous Kurdistan.

Hollande told Barzani "that France was available to support forces engaged in this battle."

IS, which proclaimed a "caliphate" straddling Syria and Iraq in late June, moved into Qaraqosh and other towns overnight after the withdrawal of Kurdish peshmerga troops, residents said.

Religious leaders said IS militants have forced 100,000 Christians to flee and have occupied churches, removing crosses and destroying manuscripts.

The UN council on Tuesday condemned attacks by IS fighters in Iraq and warned that those responsible for the violence could face trial for crimes against humanity.

The statement from the 15-member council was the second strong condemnation in as many weeks of the IS offensive that saw jihadists seize control of the main northern city of Mosul on June 10.

- Iraqi Christians targeted -

Chaldean Patriarch Louis Sako, whose church is aligned with the Roman Catholic Church, warned of a "humanitarian disaster" and called for a concerted international response.

Iraq's 400,000 Christians have been under serious threat from the IS advance and in mid-July, thousands fled the city of Mosul after the group gave them an ultimatum to convert to Islam, pay jizya (protection money) or leave on pain of death.

Francis called on the international community to "ensure the necessary help" reaches people fleeing IS fighters.

The pontiff "calls on the international community to protect all those affected or threatened by the violence, and to guarantee all necessary help" to those forced to flee their homes, "whose fate depends entirely on the solidarity of others," a statement delivered by his spokesman said.

Rights group Amnesty International said Thursday that minorities including Christians and Yazidi were "gripped by panic and fear" in the wake of the IS advance.

Many in Western Christian communities raised concerns for their Iraqi brethren.

"After the fall of Qaraqosh, which hosted refugees from Mosul and surrounding cities, majority Christians are being forced into a dramatic exodus," France's CHREDO group for the defense of eastern Christians said in a statement.

"Tens of thousands of Christians have once again been forced to flee in the greatest destitution, at the risk of their lives."

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