"It is impossible for us to stay out of it because there lies history for us," said Erdogan.

The Turkish president spoke in Istanbul during an international legal congress and told listeners Ankara was “not responsible for the results of an operation that it does not participate in".

A much-anticipated Mosul offensive to liberate the city from ISIL began midnight Sunday, according to Iraqi Prime Minister Haider al-Abadi.

In an address on state television, Abadi said only the Iraqi army and police would be in the city. He called on people in Mosul to be in solidarity with the security forces.

It was reported earlier that the Iraqi army was gradually advancing toward Mosul, which officials in Baghdad vowed to liberate by the end of the year. 

Erdogan also said the “brothers of Turkey” -- Arabs, Turkmens and Kurdish civilians -- were currently in Mosul.

Referring to a Turkish-manned military facility close to Mosul, Erdogan said: "Nobody can expect us to leave Bashiqa.”

"We trained Iraqi soldiers in Bashiqa camp, as well as peshmerga for them to fight against ISIL," Erdogan said. "If these fighters had not been there, there would not have been a decent troop to fight."

Erdogan also warned about the possibility of sectarian violence: "The insistence that Turkey be left out of the Mosul operation is because we would prevent a sectarian conflict there."

Turkish officials previously referred to troops going to Mosul to prevent any potential sectarian conflict in and around the city after it is taken from ISIL.

"We cannot say ‘yes’ to a Sunni-Shia conflict," Erdogan said.

In mid-2014, ISIL took Mosul and overran vast swathes of territory in northern and western Iraq.

Recent months have seen the Iraqi army, backed by a 60-nation air coalition led by the U.S. retake a large portion of the territory. Nevertheless, the extremist group remains in control of several parts of the country, including Mosul.