militants are suspected to have set on fire near the city of Mosul, hospital sources have said.
No deaths were reported in connection with the incident, said the sources at the hospital in Qayyara, a town south of Mosul, on Saturday. Iraqi army forces and allied militias have been battling to retake the city, Isis’s last Iraqi stronghold, since Monday.
US forces at Iraq’s Qayyara West airfield put on protective masks after winds blew fumes from the chemical plant in their direction, US military officials said. Iraqi soldiers in the area were advancing with gas masks on top of their heads, ready to pull them down, Reuters reported.
A cloud of white smoke blanketed the region to the north, where the factory is located, mingling with black fumes from oil wells that the militants torched to cover their moves.
The advance on Mosul came as the US defence secretary, Ash Carter, arrived in Baghdad to assess the campaign that began with air and ground support from the US-led coalition.
On Saturday morning, Iraqi armed troops entered into a Christian region that has been under Isis control since 2014 as part of US-backed operations to clear the entrances to the city.
A military statement said Iraqi units entered the centre of Qaraqosh, a mainly Christian town about 13 miles (20km) south-east of Mosul, and were carrying out mop-up operations across the town.
Further action was under way to seize a neighbouring Christian village, Karemlash. The region’s population fled in summer 2014 when Isis swept in.
Earlier this week, Iraqi special units also captured Bartella, a Christian village north of Qaraqosh. A US military official estimated there were fewer than 200 Isis fighters left in Qaraqosh.
The offensive on Mosul is expected to become the biggest battle fought in Iraq since the US-led invasion in 2003. The army is also trying to advance from the south and the east, while Kurdish peshmerga fighters are holding fronts in the east and north.
The Iraqi army said about 50 villages had been taken from the militants since Monday in operations to prepare the main thrust into Mosul itself, where 5,000 to 6,000 Isis fighters are thought to remain.
A US official said before Carter arrived in Baghdad: “It’s the beginning of the campaign. We do feel positively about how things have started off, particularly with the complicated nature of this operation.”
About 5,000 US personnel are in Iraq, with more than 100 embedded with Iraqi and Kurdish peshmerga forces involved in the Mosul offensive.
A US navy CPO Jason Finan was killed on Thursday by a roadside bomb in northern Iraq as he was accompanying Iraqi forces – the first American casualty of the Mosul campaign.
On Friday the militants retaliated to the advance of the Iraqi forces and the Kurdish fighters in Mosul by attacking Kirkuk, an oil city that lies east of Hawija – an area they continue to control between Baghdad and Mosul.
Authorities in Kirkuk regained control of the city on Saturday and partially lifted a curfew that was declared after the militants stormed police stations and other buildings. The region’s oil production facilities were not damaged.
At least 50 people have been killed and 80 others wounded in clashes between security forces and the militants in Kirkuk.