Syria's Assad, rebels alarmed by ISIL's advance in Iraq

Syrian rebels backed by the international community called Wednesday for help to fight the Islamic State of Iraq and the Levant in the east of the war-ravaged country.

The Free Syrian Army's appeal came a day after ISIL spearheaded a militant offensive in neighbouring Iraq that claimed the country's second-biggest city Mosul and a swathe of other northern territory.

"The Supreme Military Council calls on all friendly and brotherly Arab nations, particularly Saudi Arabia, Turkey, Qatar, the UAE and Jordan, to give aid to the brigades on the ground in Deir Ezzor province so they can confront the terrorist ISIL organisation," the FSA said in a statement.

ISIL, which emerged in the Syrian conflict in 2013, grew from al-Qaeda's Iraq affiliate, though it has since split with the network and faced criticism from its head Ayman al-Zawahiri.

It has faced a major backlash from rebels and al-Qaeda's affiliate in Syria, al-Nusra Front.

The backlash has all but forced the group from Idlib and Aleppo province, but it has entrenched itself in Raqa and the eastern province of Deir Ezzor - the scene of fierce clashes in recent weeks.

The fighting in the oil-rich province has killed more than 630 people in just 40 days and displaced more than 130,000 civilians, says the Syrian Observatory for Human Rights.

Moderate and Islamist rebels and al-Nusra Front have been battling ISIL since early January, in fighting that has killed more than 6,000 people.

However there were no major battles between ISIL and Syrian President Bashar al-Assad's army until now.

Meanwhile, the government of Assad said Wednesday it is willing to help Baghdad in the fight against "terrorism".

"The foreign-backed terrorism that our brothers in Iraq are facing is the same that is targeting Syria," said the foreign ministry.

Damascus is "ready to cooperate with Iraq to face terrorism, our common enemy", it said in a statement.

"This terrorism is a threat to peace and security in the region and the world," said the Syrian ministry, calling on the UN Security Council "to decisively condemn these terrorist and criminal acts, and to take action against the countries supporting these groups."

In Syria, Assad's government has systematically branded peaceful opponents, rebels and militants alike as "terrorists".