France on Friday called for the formation of a unity government in Iraq with or without Shia Prime Minister Nuri al-Maliki to fight Sunni jihadists advancing towards Baghdad.

Foreign Minister Laurent Fabius said the offensive by fighters from the Islamic State of Iraq and the Levant (ISIL) that has brought them close to the capital posed an unprecedented threat.

"This is the first time that a terrorist group is threatening to take control of a state," Fabius told BFM-RMC media groups.

"There has to be a government of national unity," he said. "With or without Nuri al-Maliki."

"If you want to fight terrorist groups there has to be national unity," he added.

Fabius said the situation in oil-rich Iraq was "extremely serious" with the country "on fire and with blood flowing" that threatened to have repercussions not only in Europe but the whole world.

On the question of any French intervention in Iraq, Fabius said it would only follow a request made by a "united Iraq" and if it was approved by the United Nations.

"That is not at all the case today," he said.

The militants' swift advance has sparked international alarm, with the UN's envoy to Baghdad warning that the crisis was "life-threatening for Iraq."

Analysts suggested that the country could unravel, surviving at best as a federal state.