Iraqi forces backed by tribal fighters are manoeuvring into position in the western desert bordering Syria to launch an offensive against one of the last bastions of the Islamic State group.

The jihadist group has suffered a string of defeats on the battlefield that have left in tatters its "caliphate", three years after it was declared.

After driving IS out of Nineveh province earlier this year, the Iraqi government set its eyes on Hawija, north of Baghdad, as well as the towns of Al-Qaim, Rawa and Anna in the western desert.

On Tuesday an AFP correspondent who toured the region saw several artillery units positioning themselves around Rawa and Anna, around 100 kilometres (62 miles) from the border with Syria.

Moving in clouds of dust, gunners set up their equipment in the rugged terrain and dug trenches before test-firing mortar rounds.

Further in the distance the infantry deployed, backed by tribal fighters.

Sheikh Qatari Kahlan, who commands one of the tribal units, said his forces were ready for battle.

"All the tribes wanted to take part to liberate the region and fight against IS," he told AFP.

"Tribe members inside Anna and Rawa are giving us information and assuring us that the battle will be ferocious but quick," he added, pointing an automatic rifle at the horizon.

Up ahead a few palm trees dotted an otherwise desert landscape, through which runs an asphalt road.

An Iraqi general, who declined to be named, estimated that "more than 1,500 jihadists" were in Anna, Rawa and Al-Qaim.

Al-Qaim lies closer to the Syria border and just across from Deir Ezzor province where IS jihadists are facing separate offensives from US-led Arab-Kurdish forces and government troops backed by Russia.

The Iraqi general said the battle for the three towns could begin after an expected assault on Hawija -- 300 kilometres (185 miles) -- or simultaneously.

- 'We know their methods' -

Another Iraqi commander, Qotaiba Assaad, said he expected the offensive to retake Rawa, Anna and Al-Qaim to be "quick and to our advantage".

"We have fought IS for three years and we know their methods: car bombs, snipers and bombs," said Assaad, who set up his unit in Al-Sagra a few kilometres away from Rawa and Anna.

Lieutenant Colonel Jamal Amr said huge efforts and "a real coordination between all our forces" are needed to keep the jihadists from across the porous Iraq-Syria border.

The battle for Hawija is expected to be more complicated because of its location in oil-rich Kirkuk province, which is at the centre of a long-running dispute between the Iraqi federal government in Baghdad and regional Kurdish authorities.

An offensive targeting Hawija could also be postponed due to a referendum on Kurdish independence planned for September 25 -- which Baghdad has called "unconstitutional" and "untimely".

On Tuesday Iraq's parliament voted against plans by Kurdish leaders to hold the referendum.

Iraqi forces and paramilitary units announced plans to retake Hawija on September 1, a day after recapturing Tal Afar and weeks after ousting IS jihadists from second city Mosul.

IS once held almost one-third of Iraq's territory, but the US-led coalition supporting the fight against them said after the fall of Tal Afar that the jihadists were left with no more than 10 percent of that.

Source: AFP