'Unthinkable' for Turkey to not participate in Mosul: Erdogan

President Recep Tayyip Erdogan indicated on Monday that Turkey will play a role in the US-backed Iraqi offensive to retake the city of Mosul from extremists, saying it was "unthinkable" that Ankara would stay on the sidelines.

"We will be in the operation and we will be at the table," Erdogan said in a televised speech.

"Our brothers are there and our relatives are there. It is out of the question that we are not involved."

The build-up for the offensive to retake Mosul from the Islamic State (IS) group, which has held Iraq's second city since June 2014, was marked by a bitter squabble between Ankara and Baghdad over the planning.

However, Erdogan had indicated that the issue was discussed in talks in the United States over the weekend between Turkish chief of staff General Hulusi Akar and US counterpart Joseph Dunford.

Turkey had raised concern over the possible involvement of Iraqi Shia and anti-Ankara Kurdish militia in the offensive, while Baghdad had lashed out at the presence of a contingent of Turkish troops in Bashiqa north of Mosul.

But Erdogan said the Turkish troops – whose task is ostensibly to train Sunni anti-IS fighters – were in Bashiqa to stay.

"No-one should expect us to leave Bashiqa. We are there and have made all kinds of operations against Daesh (IS)."

Our brothers are there and our relatives are there. It is out of the question that we are not involved - Recep Tayyip Erdogan

In a sign Ankara was trying to lower the temperature with Baghdad, the state-run Anadolu news agency reported that a top-level Turkish delegation was on its way to the Iraqi capital led by foreign ministry undersecretary Umit Yalcin.

Iraq's Prime Minister Haider al-Abadi announced the start of the military operation to dislodge IS from the city where its self-proclaimed "caliphate" was declared two years ago late on Sunday.

"Today I declare the start of these victorious operations to free you from the violence and terrorism of Daesh," Abadi said, using an Arabic acronym for IS.

Iraqi forces have been closing in on Mosul in recent weeks but the battle launched early on Monday is expected to be the toughest yet in the fight against IS.

Agencies contributed to this report