Iraqi forces advancing on Mosul faced stiff resistance on Monday from the Islamic State group despite an unprecedented wave of US-led coalition air strikes in support of the week-old offensive.

Federal forces and Kurdish peshmerga fighters gained ground in several areas, AFP correspondents said, but the jihadists were hitting back with shelling, sniper fire, suicide car bombs and booby traps.

IS has also tried to draw attention away from losses around Mosul by attacking Iraqi forces elsewhere, the latest coming on Sunday near the Jordanian border.

Following a weekend visit to Iraq by US Defence Secretary Ashton Carter, American officials said the coalition was providing the most air support yet.

"One week into Mosul operation, all objectives met thus far, and more coalition air strikes than any other 7-day period of war against ISIL (IS)," Brett McGurk, the top US envoy to the 60-nation coalition, wrote on social media.

"There were 32 strikes with 1,776 munitions delivered" against IS targets between October 17 and 23, coalition spokesman Colonel John Dorrian told AFP.

He said 136 IS fighting positions, 18 tunnels and 26 car bombs were destroyed.

The offensive, launched on October 17, aims to retake towns and villages surrounding Mosul before elite troops breach the city to engage die-hard jihadists in street-to-street fighting.

On the eastern side of Mosul Monday, federal troops were battling IS in Qaraqosh, formerly Iraq's largest Christian town.

Forces entered the town for the third day running but armoured convoys around it were shelled from inside the town, an AFP correspondent reported.

- Artillery support -

Federal forces also scored gains on the southern front where they have been making speedy progress, taking village after village as they work their way up the Tigris Valley.

On the northern front, peshmerga forces were closing in on the IS-held town of Bashiqa.

Turkey, which has a base in the area, said Sunday it had provided artillery support following a peshmerga request.

The presence of Turkish troops on Iraqi soil is deeply unpopular in Baghdad and the Joint Operations Command on Monday vehemently denied any Turkish participation.

But AFP reporters near Bashiqa said artillery fire from the Turkish base had been sighted several times since the Mosul operation began a week ago.

While an increasingly pragmatic IS has tended recently to relinquish some positions to avoid taking too many casualties, US officials said the group was mounting a spirited defence of Mosul.

If IS loses Mosul in Iraq, only Raqa in Syria will remain as the last major city it controls in either country.

"They have made a very good job of preparing their defences around the city," one US military official told reporters during Carter's visit.

The coalition estimates the number of IS fighters defending Mosul -- where IS supremo Abu Bakr al-Baghdadi proclaimed a "caliphate" two years ago -- at 4,000 to 7,000.

The coalition's top commander, General Stephen Townsend, said Sunday he expected not all the jihadists in Mosul would "fight to the death".

- Sowing confusion -

"By targeting the mid-tier leaders, which our special operations forces and air force have done remarkably well, we have caused a lot of confusion" in IS ranks, he said.

"I think it's going to pay off in the coming weeks."

Seeking to divert attention, the jihadists have tried to hit back with attacks elsewhere, including in the remote western town of Rutba on Sunday.

They briefly seized the mayor's office, captured and executed at least five people -- civilians and policemen -- and still controlled two neighbourhoods on Monday, army commanders said.

On Friday, IS sleeper cells in Kirkuk joined up with gunmen infiltrating the northern city in a brazen raid that saw several government buildings attacked.

The attack sparked clashes that lasted three days as security forces imposed a curfew to hunt down attackers holed up across the city.

The provincial governor, Najmeddin Karim, told AFP on Monday that the attack was over and life was returning to normal.

He said more than 74 IS militants were killed in the violence, which also left at least 46 other people dead, mostly members of the security forces.

UN refugee agency chief Filippo Grandi said in Amman on Monday that the UNHCR was preparing to receive 150,000 Iraqis fleeing the fighting in Mosul.

Human Rights Watch, meanwhile, called for an investigation into an apparent air strike that killed 15 women in a mosque in Daquq, south of Kirkuk, on Friday.

Russia has blamed the US-led coalition, which denied carrying out the air strike.

The battle for Mosul: what we know
Baghdad (AFP) Oct 24, 2016 - Iraq launched a broad offensive to retake Mosul from the Islamic State group a week ago. Here is what we know so far about the country's biggest military operation in years:

What have Iraqi forces retaken?

Federal forces operating out of the main staging base of Qayyarah have taken dozens of small villages south of Mosul and are working their way up the Tigris Valley.

After an initial push by the Kurdish peshmerga, federal army and elite counter-terrorism forces have taken over the eastern front, where they have retaken swathes of the Nineveh plain.

They wrested back control of Bartalla, a Christian town only about 15 kilometres (10 miles) east of Mosul, and are fighting to take full control of Qaraqosh, formerly the largest Christian town in Iraq.

On the northeastern front, a large deployment of peshmerga have taken several villages from IS and are closing in on Bashiqa.

The US-led coalition says it has carried out 32 air strikes on the area in a week, delivering more than 1,700 munitions that destroyed 136 IS fighting positions, 18 tunnels and 26 car bombs.

How are Iraqi forces performing?

Neither the federal government nor the autonomous Kurdish region release any figures for their dead and wounded, but both sides are taking casualties.

However, Baghdad, the Kurds and the US-led coalition supporting them with air strikes and advisers on the ground have said early gains exceeded expectations.

Kurdish leader Massud Barzani has hailed what he describes as excellent coordination with the forces from Baghdad, despite a running political and budgetary feud.

The push for Mosul, IS's last major stronghold in Iraq, has been delayed on many occasions and all sides have had ample time to learn from previous operations and fine-tune their battle plans.

How are the jihadists responding?

While an increasingly pragmatic IS has been more inclined than previously to fall back when under recent attack, it has mounted a spirited defence of Mosul so far.

The group has unleashed dozens of suicide car bombs against Iraqi forces, apparently trading land it controlled around Mosul for casualties among its enemies' ranks.

IS has lit fires in and around Mosul to obfuscate the battlefield for the aerial and satellite assets of its enemies, but that tactic is having a limited impact, analysts say.

The jihadists have also hit back by attacking Iraqi forces elsewhere, notably with a spectacular attack on the Kurdish-controlled city of Kirkuk and another on the western outpost of Rutba.

Those two operations seemed less of an attempt at making territorial gains than a bid to stretch Iraq's security forces and draw attention away from their losses in the Mosul theatre.

Medics at hospitals inside Mosul have told AFP that the number of wounded IS fighters brought in from the front lines has soared over the past week.

How are civilians affected?

Civilians are already paying a heavy price for the offensive, with tough living conditions inside Mosul deteriorating sharply and increasingly paranoid jihadists stepping up repression and intimidation.

The widespread use of smoke -- IS has set fire to tyres across the city, oil wells and trenches around it -- has led to an increase in the number of people checking in to hospitals with respiratory ailments.

More than 7,500 people have already fled the fighting and the jihadists who ruled them for two years, but Iraqi forces are still advancing in sparsely populated areas.

That figure could grow exponentially as soon as forces reach the boundaries of the city proper and attempts are to open safe corridors for the more than a million people still believed trapped in the city.