Militias backed by the Iraqi government are recruiting child soldiers from refugee camps, while mounting a key operation against Isis.

Families said young boys were taken from a camp in northern Iraq earlier this month in the latest reported use of children in Iraq, where the illegal practice has also been documented in the so-called Islamic State and the Shia militias.

Human Rights Watch (HRW) reported that residents of the Debaga camp, near Erbil in the autonomous Kurdistan region, said tribal militias recruited children among hundreds of refugees.

Iraqi forces advance to weaken ISIL stronghold of Mosul

Witnesses said Hashad al-Ashari members drove the boys to a town closer to Mosul, where the Iraqi Security Forces (ISF) are preparing to launch an offensive against the largest remaining Isis stronghold in the country.

The terrorist group has already been driven out of swathes of the country, including the cities of Fallujah, Ramadi and Tikrit.

But the gains have caused millions of Iraqis to flee their homes, including 35,000 people sheltering at Debaga after fleeing battles between government forces and Isis.

A resident told HRW that local militias had been arriving in the refugee camp with empty lorries and leaving with them filled with men and boys who volunteer to fight.

Two very large vehicles arrived on 14 August, taking around 250 new recruits, at least seven of them under the age of 18, to join forces headed by a commander known as Sheikh Nishwan al-Jabouri.

Young Iraqi volunteers were photographed training with the Popular Mobilisation Forces in Baghdad, Iraq. (AP)

Aid workers believe the boys, as young as 16, will be used to reinforce the militia’s forces near the front line.

There were allegations of complicity by Iraqi security forces after a man saw men wearing official ISF uniforms in Debaga camp days before the transfer on 14 August, as well as militia members wearing the uniforms.

The resident, who had fled the Makhmour district that Isis ruled for 21 months before they were driven out by Iraqi forces in March, said 10 of his sons had joined militias.

One of the boys is just 15, he said, but one born in 2001 “went along too but they sent him home because they said he was too young”.

His 20-year-old son said men in his group fight for one week at a time, adding: “We are fighting alongside the ISF, and our salaries are paid by Baghdad, we are basically part of the Iraqi military.”

They receive 447,500 Iraqi dinars (£290) per month, adding that at least four men in his militia had been killed and 45 wounded in the past six months.

The Hashad al-Ashari, a group of local Sunni fighters, is expected to play a key role in the operation amid rumours the government may ban the Shia Popular Mobilisation Forces after allegations of war crimes including summary killings and torture.

In pictures: Iraq battles to drive Isis out of Fallujah Show all 12 1 /12 In pictures: Iraq battles to drive Isis out of Fallujah In pictures: Iraq battles to drive Isis out of Fallujah Smoke rises after airstrikes by US-led coalition planes as Iraqi security forces advance against Islamic State extremists in Fallujah, June 15, 2016 AP In pictures: Iraq battles to drive Isis out of Fallujah Iraqi security forces advance during heavy fighting against Isis militants in Fallujah, Iraq, on 14 June AP In pictures: Iraq battles to drive Isis out of Fallujah Shia militia say that moving resources from Fallujah towards the area near Mosul was a 'betrayal' of the battle for the city GETTY In pictures: Iraq battles to drive Isis out of Fallujah Hospital sources said 18 bodies were recovered from the river over the weekend AP In pictures: Iraq battles to drive Isis out of Fallujah Up to 60,000 civilians were feared trapped in Fallujah at the start of the Iraqi operation AP In pictures: Iraq battles to drive Isis out of Fallujah Shia fighters hold an Isis flag in an operation east of Fallujah – the terror group has lost ground in both Syria and Iraq AFP/Getty In pictures: Iraq battles to drive Isis out of Fallujah Shia fighters hold their weapons as they gather near Falluja, Iraq, June 4, 2016. Reuters In pictures: Iraq battles to drive Isis out of Fallujah Pro-government forces bid to take back ground from Isis in Fallujah MOADH AL-DULAIMI/AFP/Getty Images In pictures: Iraq battles to drive Isis out of Fallujah Smoke billows on the horizon as Iraqi military forces prepare for an offensive to retake the city AP In pictures: Iraq battles to drive Isis out of Fallujah A member of the Iraqi security forces fires artillery during clashes with Isis militants near Fallujah, Iraq, 29 May, 2016 Reuters In pictures: Iraq battles to drive Isis out of Fallujah Iraqi government forces fire a rocket near al-Sejar village, north-east of Fallujah, on May 26, 2016, as they take part in a major assault to retake the city from the Islamic State group AFP/Getty In pictures: Iraq battles to drive Isis out of Fallujah Shia fighters and Iraqi security forces advance towards Fallujah Thaier Al-Sudani/Reuters

PMF fighters were also filmed training boys at an anti-Isis "summer camp" in Iraq last year, before sending them to the front line in Anbar province.

Bill Van Esveld, Human Rights Watch’s senior children’s rights researcher, said the Iraqi government and its allies must ensure that anti-Isis forces are not using child soldiers.

“The recruitment of children as fighters for the Mosul operation should be a warning sign for the Iraqi government,” he said. “The government and its foreign allies need to take action now, or children are going to be fighting on both sides in Mosul.”

Isis has carried out large-scale abductions of children and advertises its use of young boys as fighters and suicide bombers, frequently hailing them as “martyrs” on social media and featuring them in gory propaganda videos.

A United Nations protocol on the involvement of children in armed conflict, which Iraq ratified in 2008, prohibits armed groups from recruiting and using children under 18.

“As parties to the conflict, the US and other coalition members should pressure Iraq’s government and Iraqi militias to end child recruitment, immediately demobilise children, work to reintegrate them, and appropriately penalise commanders responsible for recruiting children,” a spokesperson for HRW said.

Children at an Isis training camp for children in Syria

The US-led coalition is supporting Iraqi forces and militias, launching air strikes as part of Operation Inherent Resolve and providing training, weapons and logistical support.

Britain is deploying HMS Daring, a Type 45 destroyer, and her 190 crew to the region this week and has carried out more than 900 air strikes against Isis since September 2014.

A recent tally of operations listed the bombing of militants in a cave north west of Mosul, and strikes near Qayyarah and Ramadi last week.

Air support will continue for Iraqi forces as they prepare for the long-awaited assault on Mosul, with a town and air base to the south taken from Isis on Thursday.

The UN has warned that the offensive could cause a displacement crisis on a scale not seen for “many years”, as tens of thousands of Iraqis flee their homes.

The assaults on the former Isis strongholds of Fallujah and Ramadi have seen entire districts razed to the ground, with families either shot by militants while attempting to escape or fleeing to find themselves without access to water and shelter in overcrowded camps.

Following reported abuses in Tikrit earlier this year, the Iraqi prime minister vowed not to “tolerate any violations” against civilians by militias.

Referring to allegations against the Popular Mobilisation Forces, Haider al-Abadi confirmed militia members were suspected of looting, arson and violence, sparking several arrests.