GOGJALI, Iraq (AFP) - The reclusive leader of the Islamic State in Iraq and Syria (ISIS) group broke a nearly year-long silence as Iraqi forces closed in on Mosul on Thursday (Nov 3), urging his militants to hold their ground.

It was Abu Bakr al-Baghdadi's first statement since Iraqi forces launched a massive offensive on October 17 to retake Mosul, where the ISIS chief declared the group's "caliphate" two years ago.

"Do not retreat," Baghdadi said in a purported message released by an ISIS-affiliated outlet. "Holding your ground with honour is a thousand times easier than retreating in shame."

In June 2014, days after Islamist fighters swept across swathes of Iraq, he made a rare public appearance in Mosul and announced the creation of an Islamic "state" straddling Iraq and Syria.

The "caliphate" has been shrinking steadily since last year and Iraqi forces earlier this week reached the outskirts of Mosul, the terror group's last major stronghold in Iraq.

If authentic, the recording, entitled, "This is what God and his messenger have promised us," would be Baghdadi's first since December 2015 and a rare sign of life.

Rumours have swirled about the Iraqi terror leader's health and movements, but his whereabouts are unclear.

ISIS has fallen back when massively outnumbered in recent battles, giving up some of its emblematic bastions - such as Fallujah in Iraq and Dabiq in Syria - without following its own apocalyptic ideology of fighting to the bitter end.

In his latest message, which is undated but makes reference to events that are at most a few weeks old, Baghdadi also calls for attacks against Saudi Arabia - a favourite target - and Turkey.

Ankara has troops stationed at a base just outside Mosul and Turkish President Recep Tayyip Erdogan's escalating rhetoric has raised fears of a unilateral Turkish intervention in Iraq.

Baghdadi also said that his followers who could not travel to Syria or Iraq should aim for Libya and urged all ISIS fighters to remain united in adversity.

He attempted to stir up sectarian resentment by referring to religious flags and slogans of Shi'ite fighters among Iraqi forces and by accusing other Sunni groups and politicians of treason.

The recapture of Mosul by Iraqi forces could spell the end of the group's days as a land-holding force in Iraq and deal a death blow to the "caliphate".

The US-led coalition supporting the Iraqi offensive estimates the number of ISIS fighters holed up in Mosul at 3,000 to 5,000 and has warned the battle for the city could be long and difficult.

Iraqi forces advancing on Mosul from three main fronts have retaken dozens of villages and towns scattered over hundreds of square miles.

Earlier this week, federal forces reached the eastern edge of Mosul and on Wednesday (Nov 2) were clearing the most recently reconquered areas to set up a breach of the city.

Gunfire echoed across the village of Gogjali on Mosul's eastern edge on Wednesday as elite Iraqi forces worked to clear the area.

An Agence France-Presse reporter in Gogjali, on the eastern front line, saw larger than usual numbers of civilians walking to safer areas with little or no belongings.

"Some of the kids that arrive are barefoot, and they don't have sufficient water and food," said Mr Alvhild Stromme, a media adviser for the Norwegian Refugee Council, one of the most active aid groups in Iraq.

Some were leaving Gogjali and others the eastern Mosul neighbourhood of Samah, in what may be a rare breach for civilians trapped inside the city.

All told tales of ISIS brutality.

"They confiscated my tractor and then threw me in jail for six days. They beat me and when I got out, I couldn't do my work anymore," said Mr Yusef Fariq.

The 40-year-old farmer, speaking from his home in Gogjali and surrounded by his mother and two sons, still had the long beard ISIS militants forced him to grow.

"They were killing us, always asking for money, we couldn't go anywhere. We went through hell," his mother said.

With an assault on the city looking imminent, aid groups said they were "bracing for the worst" and warned that the fate of a million-plus civilians still believed trapped inside Mosul was in the balance.