Iraqi forces on Friday entered Al-Qaim, the main town in the Islamic State group's last bastion in the country, military commanders said.
Early Friday morning, Iraqi forces unleashed a barrage of artillery fire against jihadist positions inside the town, backed by Iraqi and US-led coalition air strikes.
Troops from the army and the elite Counter Terrorism Service "have started the assault on the centre of Al-Qaim," Staff Major General Noman Abed al-Zobai, the commander of the 7th Division, told AFP from the scene.
Shortly afterwards, another officer said on condition of anonymity that the town's Gaza district had fallen from jihadist hands.
"Counter Terrorism Service units and tribal fighters have liberated Gaza after violent clashes, leaving some terrorists dead, while others withdrew towards the centre of Al-Qaim," he said.
The paramilitary Hashed al-Shaabi (Popular Mobilisation) force said in a statement that jihadists had set fire to civilians' houses in the southwestern neighbourhood to make it hard to see them from the air.
Government forces launched the operation last week to seize Al-Qaim and its surroundings, a pocket of barren desert along the Euphrates river near the border with Syria.
Home to around 150,000 people, it is the last Iraqi remnant of the self-styled caliphate IS declared after rampaging across Iraq and Syria in 2014.
The US-led coalition has said around 1,500 IS fighters are left in the area, which it expects to be the scene of the "last big fight" against the group in Iraq.
IS is also under pressure from separate offensives by Syrian regime and US-backed forces in the neighbouring Syrian province of Deir Ezzor.
The Hashed said on Friday several IS fighters had fled across the border towards the Syrian town of Albu Kamal.