US troops can also accompany the conventional Iraqi army, but at much farther distances.

"The retaking of Isis's northern Iraq stronghold, Mosul, may lead to the return to Europe of violent ISIS-fighters", Commissioner Julian King told German newspaper Die Welt on Tuesday.

Since it was captured at lightning speed by ISIS fighters in June 2014, Mosul has been a vital stronghold in the terror group's self-declared caliphate, holding strategic and symbolic importance. But ahead of the offensive, Turkey and Iraq were entangled in a war of words over Turkey's presence in northern Iraq. Yildirim was responding to a question about a statement he made on Turkish jets participating in the operation.

Yildirim told his MPs that Turkey continuously cautioned the United States and the European Union about the region's sensitivities.

Even a small number of militants would pose "a serious threat that we must prepare ourselves for", said Julian King in an interview with Germany's Die Welt newspaper published on October 18.

The Iraqi Army's 9th Division meanwhile reached the outskirts of the town of al-Hamdaniyah, south of Mosul, but stopped advancing because of snipers and suicide bombers, according to a military officer.

During the first day of the operation, the most complex for Iraq's military since the withdrawal of USA troops in 2011, Kurdish forces say they retook nine villages and pushed the frontline back eight kilometers (five miles). Baghdad denies it granted permission and has ordered the Turks to withdraw - a call Ankara has ignored.

Death toll at 23 in hospital fire in eastern India
He said two of the critically injured patients have been admitted in the ICU of Capital Hospital. Dozens of patients were taken to other medical facilities in the city.

It will involve more than 25,000 troops, including the Iraqi army, the Kurdish peshmerga, Sunni tribal fighters and Shiite militias.

Brig. Gen. Haider Fadhil said his men had planned to move at dawn, but postponed the operation in the oil-rich capital of Nineveh province, the New York Times reported.

The large and complex operation to recapture Mosul, Iraq's largest city, began Monday and is expected to last weeks or months. ISIS resistance has come in the form of mortar and small arms fire, IEDs and suicide vehicle bomb attacks.

Terror group Islamic State is "failing" in Iraq, Defence Secretary Michael Fallon has said - as he warned that the fight to regain the country's second largest city "will not be a quick operation".

The source said that several Iraqi government troops were killed by an IED on Tuesday along the southern frontline of the battle.

Since then, ISIS has gradually lost its other Iraqi cities - Ramadi, Tikrit and Falluja - to government forces, with the government's eye ultimately on recapturing the country's second city of Mosul, once a cosmopolitan trade hub of two million residents.