Iraqi forces were inching to within striking distance of eastern Mosul Tuesday as coalition defence chiefs gathered in Paris agreed to also take on the jihadists' Syrian bastion of Raqa.

With the Mosul battle in its second week, French President Francois Hollande called for the US-led coalition against the Islamic State group to prepare for the aftermath and the next stages of the campaign against the jihadists.

The United Nations said it had received reports of a new series of atrocities by the jihadists as troops close in on its last major urban stronghold in Iraq.

Forces from the elite counter-terrorism service (CTS) retook areas close to the eastern outskirts of Mosul.

"On our front, we have advanced to within five or six kilometres (three to four miles) of Mosul," their commander, General Abdelghani al-Assadi, told AFP.

"We must now coordinate with forces on other fronts to launch a coordinated" attack on Mosul, he said, speaking from the Christian town of Bartalla.

Kurdish peshmerga forces are making gains on the northeastern front, but federal forces advancing from the south have some way to go before reaching the outskirts.

"All axes of advance have made the progress we expected at this stage of the operation, some are ahead of schedule," said Brett McGurk, the US envoy to the coalition.

Meanwhile, thousands of men from the Hashed al-Shaabi paramilitary umbrella group dominated by Tehran-backed Shiite militias were preparing for a push to the west of mainly Sunni Mosul.

- Turkey threat -

The Hashed's mission will be to "cut off and prevent the escape of (IS) towards Syria and fully isolate Mosul from Syria", said Jawwad al-Tulaibawi, spokesman for the Asaib Ahl al-Haq militia.

"We expect that it will be a difficult and fierce battle," he said.

Iraqi Kurds and Sunni Arab politicians have opposed the Hashed's participation in the operation, as has Turkey, which has a military presence east of Mosul despite repeated demands by Baghdad to withdraw its forces.

Tensions have risen between Baghdad and Ankara, whose foreign minister, Mevlut Cavusoglu, warned Tuesday that if there is a threat to Turkey, "we are ready to use all our resources including a ground operation".

As Iraqi forces advance, the United Nations said it has received reports of dozens of execution-type killings by IS in Nineveh province, of which Mosul is the capital.

Citing preliminary reports, the UN said those killed included 50 police officers who had been held hostage.

In Paris, French Defence Minister Jean-Yves Le Drian was meeting coalition counterparts, including Pentagon chief Ashton Carter, to review the war on IS after more than two years of air strikes, training and on-the-ground military advisers.

Besides coordinating their support for the forces closing in on Mosul, ministers also discussed the Syria side of the campaign and said they were "laying the groundwork" for the isolation of Raqa.

France is keen to tackle Raqa, where the 3,000 to 4,000 IS fighters include a contingent of around 300 French nationals whose potential return to France when the "caliphate" disintegrates is considered a major national threat.

- Looking to Raqa -

As the ministers met, Hollande warned that "the recapture is not an end in itself. We must already anticipate the consequences of the fall of Mosul."

"What is at stake is the political future of the city, the region and Iraq," Hollande said, calling for "all ethnic and religious groups" to have a say in the future running of Mosul.

Seeking to draw attention away from the Mosul campaign, IS has staged attacks in the northern city of Kirkuk and western town of Rutba in recent days.

Jihadists seized two neighbourhoods in Rutba, but officials said that as of Tuesday it was fully back in government hands.

Senior Iraqi and US military officials have reported that IS leaders are already trying to leave Mosul to reach the Syrian side of their "caliphate".

But an official close to Le Drian said a few hundred IS fighters recently moved in the opposite direction, reinforcing the estimated 3,000 to 5,000 jihadists defending Mosul.

IS had shown increasing pragmatism in recent battles, tending to fall back in the face of superior firepower.

But with its claim to run a "caliphate" losing credibility with every new loss of territory, IS has mounted a fierce and well-organised resistance in the fight for Mosul.

The city is where IS supremo Abu Bakr al-Baghdadi proclaimed the cross-border "caliphate" in June 2014, and its loss could spell the end of the group's days as a land-holding force in the Iraqi part.

In Moscow Tuesday, Russian Foreign Minister Sergei Lavrov equated US support for Iraqi efforts to recapture Mosul with Russian backing of a Syrian government offensive to seize rebel-held east Aleppo.