Iraqi forces on Sunday pounded the Islamic State group in Tal Afar, one of its last bastions in the country, in a new assault just weeks after ousting IS from second city Mosul.

Once a key IS supply hub between Mosul -- around 70 kilometres (45 miles) further east -- and the Syrian border, Tal Afar is the last major population centre in northern Iraq under jihadist control.

Weeks after recapturing Mosul in a major blow to the jihadists, convoys of Iraqi forces around Tal Afar began pounding IS positions from three sides at dawn Sunday.

An AFP correspondent reported mortar fire in the mostly desert area dotted by some farmland, with columns of smoke billowing skywards.

Prime Minister Haider al-Abadi announced the offensive in a pre-dawn televised speech.

Wearing black military fatigues and standing in front of an Iraqi flag and map, he announced "the start of an operation to free Tal Afar".

"I am saying to Daesh that there's no choice other than to leave or be killed," he said, using an alternative acronym for IS.

"We have won all our battles, and Daesh have always lost," he said, telling his troops: "The entire world is with you."

Several hours after the battle began, the federal police said it had retaken the village of Al-Abra Al-Sghira west of Tal Afar.

The US-led coalition fighting IS in Iraq and Syria welcomed the start of the offensive and pledged support to Iraqi forces involved.

The "operation to liberate Tal Afar is another important fight that must be won to ensure the country and its citizens are finally free of ISIS", the head of the anti-IS coalition Lieutenant General Stephen Townsend said in a statement, using another acronym for IS.

- Coalition support -

"The coalition is strong, and fully committed to supporting our Iraqi partners until ISIS is defeated and the Iraqi people are free," he said.

The coalition would continue to support Iraqi forces with "equipment, training, intelligence, precision fires and combat advice".

IS in June 2014 overran Tal Afar, a Shiite enclave in the predominantly Sunni province of Nineveh, on the road between Mosul and Syria.

At the time, its population of around 200,000 was overwhelmingly Turkmen, one of Iraq's largest ethnic minorities.

Tal Afar's Shiites were directly targeted by IS, while some members of its Sunni minority joined the jihadists and went on to form a contingent with a particularly brutal reputation.

According to the coalition, between 10,000 and 50,000 civilians remain in and around the city.

Un Humanitarian Coordinator for Iraq Lisa Grande said Sunday that "more than 30,000 people have already fled" the Tal Afar region and that thousands more were expected to seek to flee.

"Families are trekking for 10 to 20 hours in extreme heat to reach mustering points. They are arriving exhausted and dehydrated," Grande said in a statement.

"We don't know how many civilians are still in the areas where fighting is occurring, but we are preparing for thousands more to flee in coming days and weeks."

Authorities have accused the approximately 1,000 jihadists in the city of using civilians as human shields during Iraqi and coalition air strikes earlier this week in preparation for the ground assault.

Abadi said that Iraq's Hashed al-Shaabi paramilitary forces would help army, police and counter-terrorism units to retake Tal Afar.

- 'Victory is near' -

The umbrella organisation, which is dominated by Iran-backed Shiite militias, has already been fighting to retake other Iraqi cities from IS.

"In the early hours, the guns and flags turned towards their targets," said Hashed spokesman Ahmed al-Assadi.

"Victory is near" in Tal Afar, an "Iraqi city taken hostage and humiliated for years by attacks from these barbarians", he said.

Even before Abadi's announcement, Iraqi planes had dropped leaflets to residents in Tal Afar and its surroundings, the Hashed said in a statement.

The authorities said they had set up a radio station to keep residents briefed.

IS overran large areas north and west of Baghdad in 2014, but Iraqi forces have since regained much of the territory.

Once Tal Afar is retaken, Iraqi authorities intend to turn their sights south to jihadist-held Hawijah in the province of Kirkuk, 300 kilometres (185 miles) northwest of Baghdad.

Jihadists also still hold areas of Anbar, a western province that borders Syria and faces major security challenges.

As well as in Iraq, IS has suffered major setbacks in Syria, where US-backed fighters have retaken more than half of its de facto Syrian capital Raqa.

Russia-supported Syrian troops have almost entirely encircled IS in Syria's central desert region, and the jihadists are also facing twin assaults from the Lebanese army and Shiite movement Hezbollah on the Lebanon-Syrian border.

source AFP