The UN Security Council met Thursday in emergency session to address the crisis sparked by the jihadist offensive in Iraq, with France and the United States weighing action.

French President Francois Hollande offered to support forces combating the fighters during talks with Kurdish leader Massud Barzani while the US administration reportedly was considering air strikes to shore up Iraqi forces.

Pope Francis called on the world to protect Christians after Islamic State (IS) fighters seized Iraq's main Christian city of Qaraqosh, forcing tens of thousands to seek refuge.

The 15-nation Council was meeting behind closed doors at UN headquarters in New York, at France's request.

Ambassadors were to hear a report by a top UN official on the IS advance that has brought the al-Qaeda affiliate within striking distance of the main Kurdish city of Arbil.

"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 Paris.

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

In Washington, the White House said the IS advance could unleash a "humanitarian catastrophe" but declined to confirm reports that President Barack Obama was considering air strikes.

"I'm not in a position to rule things on the table or off the table in this context," said spokesman Josh Earnest.

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.

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 minorities trapped -

UN Secretary General Ban Ki-moon said he was "appalled" by reports of attacks by IS fighters, noting that Christian, Turkmen and Yazidi minorities were mostly affected.

"Reports of Yazidis amassing along the Turkish border as well as thousands also trapped in the Sinjar mountains in desperate need of humanitarian assistance are of urgent and grave concern," said Ban.

Saying he welcomed past airdrops to trapped civilians, Ban called on all governments to "help alleviate the suffering of the population affected by the current conflict in Iraq."

US officials raised concern for the fate of thousands of Yazidis trapped for days on a mountain near Sinjar, without food, water and shelter, and surrounded by Islamic militants.

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.

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

Turkey said Thursday it had taken in up to 800 people from Iraq's Yazidi, a minority who adheres to an ancient faith rooted in Zoroastrianism but are considered heretics by the Islamists.

Foreign Minister Ahmet Davutoglu held a three-hour long crisis meeting Thursday with military and intelligence chiefs to discuss the potential fallout from Iraq.

The government is also planning to establish a 20,000-capacity camp in the Iraqi Kurdish city of Dohuk for Iraqi Turkmens.