US Defence Secretary in Iraq as anti-IS forces advance on Tal Afar

US Defence Secretary Jim Mattis arrived in Iraq on Tuesday on an unannounced visit to discuss efforts to combat the Islamic State group.

Mattis' arrival comes just days after Baghdad launched a fresh assault on the IS group's urban stronghold of Tal Afar in northern Iraq.

Despite Iraqi forces making early gains in the battle that began on Sunday, Mattis has warned that the extremist group is far from defeated.

Brett McGurk, US special envoy to the coalition against IS, told reporters that Iraqi forces had retaken 235 square kilometers (90.7 miles) in the battle's first 24 hours.

Mattis will meet Iraqi Prime Minister Haidar al-Abadi and Defense Minister Arfan al-Hayali to discuss the future of US involvement in Iraq following the defeat of IS, US officials told Reuters.

The officials, who spoke on condition of anonymity, said that despite Iraqi forces clearing IS fighters from major cities like Mosul, concerns remain about their ability to hold territory.

US officials believe that IS still maintains cells in Mosul that continue to pose a threat to the city's security.

With the extremist group now sinking further into the Euphrates valley region of Syria, US officials are hoping to catch the militants on their retreat. Mattis has said that the next step for anti-IS forces would be to move on the middle Euphrates valley, where IS fighters are holed up in the Syrian town of Deir al-Zour.