the first phase of a long-planned offensive to retake the city from Islamic State.
The advance on Monday evening aims to liberate the city, an Isis stronghold, more than two years after Abu Bakr al-Baghdadi declared the establishment of a caliphate from there. The Iraqi army has also moved into villages to the south of the city, where local tribes ousted Isis on their own.
The Kurdish forces, known as peshmerga, advanced steadily in long armoured columns across the Nineveh plain to the east of Mosul, pausing at each deserted village to allow engineers to search for mines and booby traps left by Isis.
Peshmerga officials claimed their tanks had destroyed two Isis suicide truck bombs. By the end of the first day in the attempt to oust the jihadi group from their last major Iraqi stronghold, Kurdish leaders said their forces had captured 200 sq km (77 sq miles).
Most of the local population on the Nineveh plain has fled since Isis seized the area in the summer of 2014. The Guardian has attempted to contact locals still in Mosul city, but phones were either switched off or lines went dead within seconds.
Under a US-brokered agreement negotiated in the run-up to the offensive, the peshmerga and Shia militias are supposed to stop short of entering Mosul itself, which is mostly Sunni, allowing Sunni-led Iraqi forces to occupy the city in an effort to minimise sectarian conflict in the aftermath of the battle against Isis.
US, British and French special forces are playing a supporting role in the offensive, some giving coordinates on enemy targets for airstrikes. An ABC correspondent covering the peshmerga advance reported that US troops from the 101st Airborne Division were operating openly with the Kurds.
Addressing his troops at Khazer, east of Mosul, the president of the Iraqi Kurdistan region, Masoud Barzani, said: “This is the first time the peshmerga and Iraqi forces have worked together against Daesh [Isis] … we hope this will become a concrete foundation for our future relations with Baghdad.
“The liberation of Mosul is not an end to terror and terrorism but this was a good lesson so in the future we will resolve our differences through understanding and working together. We reassure the people of Mosul that both the peshmerga and the Iraqi army will do everything not to cause any loss to the people and no revenge killing will take place.”
Lt Gen Stephen Townsend, the commander of US military operations against Isis, said in a statement: “This operation to regain control of Iraq’s second-largest city will likely continue for weeks, possibly longer. Iraq is supported by a wide range of coalition capabilities, including air support, artillery, intelligence, advisers and forward air controllers.
“But to be clear, the thousands of ground combat forces who will liberate Mosul are all Iraqis.”
The UN high commissioner for refugees (UNHCR) warned that up to 100,000 Iraqis may flee to Syria and Turkey to escape the battle for Mosul, and the organisation appealed for an additional $61m (£50m) to provide tents, camps, winter items and stoves for displaced people inside Iraq and new refugees needing shelter in the two neighbouring countries.
The start of the offensive, which has been months in the planning, was announced in an address on state television by Iraq’s prime minister in the early hours of Monday morning. Haider al-Abadi said: “We have been battling Isis for more than two years. We started fighting Isis in the outskirts of Baghdad, and thank God we are now fighting them in the outskirts of Mosul and, God willing, the decisive battle will be soon.
“These forces that are liberating you today, they have one goal in Mosul, which is to get rid of Daesh and to secure your dignity. They are there for your sake.”
After a month-long buildup, the last urban stronghold of Isis in Iraq has for several days been almost completely surrounded by a 30,000-strong force.
On Monday morning just before dawn, columns of peshmerga fighters could be seen lined up for the offensive to the north-east of the city. The forces had taken control of seven villages and the main road linking Mosul with the Iraqi Kurdish regional capital, Irbil, by 10am BST, Turkey’s state-run news agency reported.
Soldiers had earlier stood by bonfires singing battle hymns while in the distance the sound of airstrikes reverberated along with a regular artillery barrage.South of the city, Iraqi forces, which had driven hundreds of miles for what Baghdad has hailed as a last battle against the terrorist group, moved into their final positions on Friday.Skirmishes have flared outside Mosul over the last few days with an airstrike on one of its main bridges on Sunday. It is not clear who was responsible for the strike on the al-Hurriya bridge but Amaq, the news agency associated with Isis, blamed US forces. It is thought that the destruction of the bridge could hinder Isis fighters trying to flee the city.
Early on Monday, a dense, noxious haze hung over the mountains and the plains leading to Mosul – caused by oil fires lit by Isis in anticipation of the attack.
Isis is believed to have heavily mined the roads leading into its territory with large numbers of improvised devices and the Iraqi government has previously warned Mosul residents to stay in their homes.
In a reflection of the widespread concern over potential sectarian conflict once Isis is ousted, the Saudi foreign minister, Adel al-Jubeir, said on Monday that Mosul would turn into a bloodbath and descend into mass killings if the Iraqi government allowed Shia militias to enter the city.
In a rare press conference in London, Jubeir said: “We oppose any kind of involvement by the Shia militias. If they go into Mosul ... I would expect the negative reaction will be tremendous and if there are mass killings, it could end up being a bonanza for violent extremists, and recruitment for Daesh. It could add fuel to the sectarian fires raging in the region and so we have urged the Iraqi government not to use the Shia militias. That is the greatest danger that we see.”
He said that although there had been reassurances from the Iraqi government about the deployment of Shia militias, he was not sure the Iraqi government was fully in control.