Iraqi armed forces have started an offensive to dislodge ISIL fighters from an area on the border with Syria, south of the Euphrates river.

The offensive, which began on Saturday, is supported by a US-led air alliance. It is also aimed at tightening Iraq's hold on its border with Syria, a spokesman for Iraq's Joint Operations Command, Brigadier Yehia Rasool, said in a statement.

"Iraqi forces are progressing towards the specified aim of cutting routes leading to Akashat and controlling the international borders with Syria in order to prevent terrorists' infiltration," he said.

The offensive in the Akashat region, which has natural gas reserves, is meant to pave the way for the seizure of ISIL-held towns in the Euphrates river valley, including the border post of al-Qaim, military statements said.

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Saturday's offensive follows a series of military setbacks suffered by the Islamic State of Iraq and the Levant, also known as ISIS, in Iraq.

In July, Iraqi forces retook control of Mosul, ISIL's key stronghold in the north, after a campaign of nearly nine months.

In August, Iraqi Prime Minister Haider al-Abadi declared victory over the group in Tel Afar, west of Mosul.

ISIL still controls Hawija in Iraq's oil-rich province of Kirkuk and western areas in the country's largest province of Anbar.