Feuding Iraqi politicians should unite as a crucial operation to retake the city of Mosul from the Islamic State group draws near, a top US envoy said Thursday.

The latest turmoil in Baghdad saw a bitter row break out between Iraq's defence minister and parliament speaker, who are also the country's most prominent Sunni politicians.

The White House's special envoy to the coalition battling IS, Brett McGurk, said he had so far seen no impact on the campaign but called for greater cohesion ahead of Mosul.

"I will say when it comes to Mosul it'll be really important for Iraqi leaders to stay focused and be pulling together to get this right," he told reporters in Baghdad.

"It's not just a military campaign, which we're confident will go well, it's also the humanitarian element to make sure that IDPs (internally displaced persons) are taken care of and then the stabilisation to make sure that the ground is laid to return the people to their homes," he said.

Earlier this month, Defence Minister Khaled al-Obeidi accused speaker Salim al-Juburi of corruption, the row escalating in a travel ban on the head of the legislative house.

The judiciary since dropped the case against him after an expeditious hearing but the feud does not bode well for efforts to unite Sunni leaders in the run-up to an operation on Mosul.

Mosul, the country's second city, has been the main jihadist hub in Iraq since the Islamic State group seized it and proclaimed its "caliphate" more than two years ago.

The number of different players involved in the northern region and the scope of the likely population displacement will make an assault on Mosul Iraq's most challenging operation since it started fighting back against IS.

Prime Minister Haider al-Abadi has vowed Iraq would be rid of IS by the end of the 2016 but McGurk refrained from giving a specific timeframe.

"The liberation of Mosul is coming, we are now approaching the final phase of the planning and the liberation is coming, and it's about time," the US envoy said.

Source: AFP