In his first message after Iraqi forces started an offensive to take back Mosul, Islamic State leader Abu Bakr Al-Baghdadi has expressed confidence of victory.

Mosul is the last major city under control of his group in Iraq and there are an estimated 5,000 IS fighters holed up in the city.

Al-Baghdadi also called on Islamic State fighters to invade Turkey, according to a Reuters report.

He said that "holding your ground in honour is a thousand times better than retreating in disgrace."

The media arm of the IS released the audio message. It's the first recording reportedly of Al-Baghdadi released since late 2015.

Meanwhile, the Iraqi army has been trying to consolidate its most recent gains in the offensive by combing the streets of the recaptured Kukjali district for any remaining IS fighters, said a BBC report.

The army is moving with caution, amid fears of ambushes, secret tunnels and booby traps, it said.

The elite Counter-Terrorism Service (CTS) troops retook the eastern Kukjali area and reached the more built-up Karama district, on Tuesday.