US soldiers at a base near the northern Iraqi city of Mosul have donned protective masks against toxic fumes from a sulphur plant set alight in fighting with so-called Islamic State.

They took the precaution after the wind blew smoke from the fire towards Qayyarah air field.

US Defence Secretary Ash Carter is in Baghdad on an unscheduled visit.

Meanwhile, advancing Iraqi forces entered the town of Qaraqosh, 32km (20 miles) south of Mosul, commanders say.

Qaraqosh, Iraq's largest Christian town before the war, is said to be largely empty but IS has laid landmines on the approaches to Mosul.

The militants have been attacking with suicide bombers elsewhere, driving vehicles laden with explosives at high speed towards government lines.

Friday's IS attack on the city of Kirkuk, 170km (105 miles) south-east of Mosul, now appears to be over, leaving at least 35 people dead and 120 wounded, according to medical sources.

Qayyarah acts as the main US hub for supporting the Iraqi government offensive to drive IS out of their Mosul stronghold.
The fire began two days ago, when IS fighters reportedly set the sulphur plant alight in Mishraq, south of Mosul.

"The winds have actually shifted south, so, as a precautionary measure, the troops at Qayyara West have donned their personal protective equipment - continuing their operations at this point in time," an official told Reuters news agency, speaking on condition of anonymity.

An Iraqi commander, Qusay Hamid Kadhem, told AFP news agency two civilians had died from the fumes and "many others" had been injured.

A similar fire at the Mishraq plant in 2003 burnt for weeks, sending huge amounts of sulphur dioxide into the air. It caused respiratory problems for local people and damaged the environment.

How harmful can sulphur dioxide be?

Sulphur dioxide gas is toxic when inhaled or when the skin or eyes are exposed.
When inhaled, it causes irritation to the nose and throat. Exposure to high concentrations causes nausea, vomiting, stomach pain and corrosive damage to the airways and lungs.
Skin contact causes stinging pain, redness of the skin and blisters, while eye contact causes watering and, in severe cases, may cause blindness.