Iraqi military operations to retake the contested Baiji oil refinery were underway on Wednesday.
Shia militia, known as Popular Mobilisation Units, were filmed firing rifles and rockets at alleged Islamic State (Isil) group positions in the area.
A member from the Iraqi security forces guards as smoke rises from Baiji oil refinery
The fighting took place just hours after the Iraqi government announced the start of a wide-scale operation to recapture areas under the control of the Isil in western Anbar province.
The IS-held town of Baiji and its refinery is seen as a key step in the fight against Isil, who rely on it as a major source of revenue. It is Iraq's largest oil refinery.
An Iraqi army member mans a tank on the outskirts of Baiji refinery
US defence officials said last week that Iran had also entered the fight to retake Baiji from IS, contributing small numbers of troops - including some operating artillery and other heavy weapons - in support of advancing Iraqi ground forces.
Baiji is 145 kilometres (90 miles) south of Mosul and 250 kilometres (155 miles) north of Baghdad.
