Thursday's attack came as a major offensive by Iraqi forces and their allies to retake Mosul from IS militants is now in its third week.

After a almost year-long silence, Abu Bakr al-Baghdadi, the self-declared caliph of the Islamic State, released a blistering audio recording imploring his forces to remain firm in the face of the US-backed Iraqi offensive in Mosul and excoriating those who might consider fleeing.

"Oh you who seek martyrdom!"

In the recording, al-Baghdadi, rallies fighters especially in Mosul, calling on them to obey orders while remaining resilient and steadfast. "Start your actions! Turn the night of the disbelievers into day", he says, according to a translation provided by the SITE Intelligence Group, a US organization that monitors militant activity online which reported the al-Baghdadi recording first.

Iraqi special forces say they have begun their assault into more urban neighborhoods of Mosul from its easternmost district, its latest push to drive Islamic State fighters from the city.

"Totally decimate their territories, and make their blood flow like rivers", al-Baghdadi also says.

Iraqi special forces have swung around to attack Islamic State militants in Mosul from a new entry point, to the city's northeast.

Mosul was captured by the IS group in June 2014, after which Baghdadi declared his "caliphate" from a mosque in the city. The special forces fired a rocket that blew up the vehicle, killing the attacker. Gen. Haider Fadhil said, but that vehicle managed to get away.

Fadhil says a second vehicle that emerged from the same area, presumably another suicide auto bomber, managed to get away.

A parallel operation to retake Raqqa, Islamic State's de-facto capital in Syria, is also expected to be launched in the coming weeks by the USA -led military coalition.

By midday, Iraqi forces continued to consolidate their gains, looking for any IS fighters who may have stayed behind, checking houses and streets for booby traps, and handling an influx of hundreds who fled IS-held territory deeper in the city.

Baghadi told his followers to launch "attack after attack" in Saudi Arabia, targeting security forces, government officials, members of the ruling Al Saud family and media outlets, for "siding with the infidel nations in the war on Islam and the Sunna (Sunni Muslims) in Iraq and Syria".

He calls on fighters to "respond to all attacks", and to "target all in their media and forces, and all who belong to them".

In the unverified recording shared by followers, Baghdadi told ISIS fighters to "unleash the fire of their anger" on Turkish soldiers who are waging war against the group in Syria and urged them to take the battle to Turkey.

Several explosives-laden vehicles tried to attack the troops but were destroyed, including a bulldozer that was hit by an airstrike from the USA -led coalition supporting the offensive.

Iraq's military and Kurdish Peshmerga-backed by USA special forces and other troops- began a ground offensive just over two weeks ago with the goal of retaking the city that Islamic State overran two years ago.

As Iraqi forces move westward into Mosul, thousands of people have been displaced and are moving further east for shelter.