Mines and other ordnance buried by jihadists is slowing an advance by Iraqi forces in the country's western desert bordering Syria against one of the Islamic State group's last outposts.

"We're just a few hundred metres from (the town of) Anna but our biggest obstacle are mines and explosive devices planted by Daesh," Colonel Ahmad al-Dulaimi told an AFP reporter at the scene, using an Arabic acronym for IS.

Members of Iraq's security forces and allied paramilitary units of the Hashed al-Shaabi, their uniform splattered in ochre, were making painfully slow progress, with some military vehicles sinking in the sand.

Anna, surrounded to the east, west and south, sat among scrawny trees on the horizon.

Black smoke billowed over the town from barrels of oil set ablaze by IS fighters to obscure the skies for US-led coalition warplanes and Iraqi helicopters supporting the Iraqi advance, amid intermittent automatic weapons fire.

General Abdelamir Yarallah, head of the anti-IS Joint Operations Command, announced Tuesday that "infantry units and armour backed by the Hashed al-Shaabi" had launched an offensive to retake Anna and nearby Al-Rayhanna village.

Anna, about 100 kilometres (60 miles) west of the border with war-torn Syria, is one of three towns in Anbar province of western Iraq still under IS control.

After Anna, Iraqi forces are expected to next target Rawa to the northwest and finally Al-Qaim, close to the border with the Syrian province of Deir Ezzor.

IS is under fire across the border in twin offensives mounted by forces loyal to Syrian President Bashar al-Assad and a Kurdish-Arab alliance backed by the United States.

Three years after IS took control of swathes of territory straddling the two Arab states, Iraqi forces are pushing to retake all areas seized by the jihadists, scoring their biggest victory in July with the recapture of the country's second city Mosul.

Iraq is also preparing to launch an assault against another of the jihadists' last remaining strongholds, the town of Hawija about 300 kilometres north of Baghdad.

Source: AFP