U.S. 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, BBC News reports.

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

In Baghdad, Turkish attempts to join the offensive against IS were rebuffed.

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

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.