France has said it is ready to welcome Christians fleeing the area of Iraq controlled by Islamic State group's fighters, saying it is "outraged" by their persecution.

Islamic State fighters seized large swaths of northern Iraq last month, prompting hundreds of Christian families in Mosul to flee a city which has hosted the faith since its earliest years.

"France is outraged by these abuses that it condemns with the utmost firmness," Laurent Fabius, France's foreign minister, and Bernard Cazeneuve, the interior minister, said in a joint statement on Monday.

"The ultimatum given to these communities in Mosul by ISIL is the latest tragic example of the terrible threat that jihadist groups in Iraq, but also in Syria and elsewhere, pose to these populations that are historically an integral part of this region," they added, referring to the Islamic State's former name of Islamic State of Iraq and the Levant.

"We are ready, if they wish, to facilitate their asylum on our soil.

"We are in constant contact with local and national authorities to ensure everything is done to protect them," both ministers said.

UN denounces minority persecution

Islamic State had ordered Christian families to convert to Islam or leave the city, prompting the mass exodus.

The ultimatum given to these communities in Mosul by ISIL is the latest tragic example of the terrible threat that jihadist groups in Iraq, but also in Syria and elsewhere, pose to these populations that are historically an integral part of this region. - Statement by Laurent Fabius and Bernard Cazeneuve, France's foreign and interior ministers

Those who failed to comply were threatened with execution, and the property of those who left was forfeited to the Islamic State, AFP reported a statement from the group as saying.

The United Nations Security Council has already denounced the persecution of minorities in Iraq, warning such actions can be considered crimes against humanity.

In a unanimous declaration adopted last week, the Council condemned "in the strongest terms the systematic persecution of individuals from minority populations and those who refuse its extremist ideology in Iraq by ISIL and associated armed groups", it said.

Islamic State has also persecuted Iraq's majority Shia Muslims in areas under their control, as well as Sunni Muslims that oppose the group's ideology.

Iraqi Prime Minister Nouri al-Maliki earlier this month condemned the treatment of the Christians and instructed a government committee to help those made homeless.

Before the 2003 US-led invasion, more than a million Christians lived in Iraq, including more than 600,000 in Baghdad and 60,000 in Mosul, as well as a substantial number in Kirkuk and in Basra.