Abu Ahmed drove all night and half-way across Iraq to bring the meat stew and rice in the back of his pickup truck to fighters on the Mosul front lines.

Seven hours after leaving the Shiite holy city of Najaf in a convoy, he stopped under a road sign saying the northern city of Mosul, the Islamic State group's last major stronghold in Iraq, was 59 kilometres (36 miles) away.

As he unloaded the food from his truck, Abu Ahmed, a white scarf wrapped around his head, said he had come to "bring his support" to the Iraqi forces that have been fighting on Mosul's southern front for two weeks.

The convoys known as "mawakeb" have been relentlessly delivering food, water, juice, tea, clothes and other basic supplies to the fighters battling the jihadists of the Islamic State (IS) group.

"They are heroes who are sacrificing their lives for us, so we are supporting them in whatever way we can, such as by cooking for them," said another member of the convoy, Ryad al-Attabi.

The 42-year-old car dealer left his wife and children in Baghdad to spend a week behind the front lines, serving food to pro-government fighters.

The mawakeb, a religious term that usually describes services volunteered to Shiite pilgrims, have become an informal but effective organisation that forms an integral of the war effort.

In June 2014, the most revered Shiite cleric in the country, Grand Ayatollah Ali al-Sistani, urged Iraqis to take up arms against IS, which had swept across the Sunni Arab heartland and was threatening Baghdad and Shiite holy cities in the south.

That call for jihad (holy war) saw the emergence of the Hashed al-Shaabi (Popular Mobilisation), a mix of volunteers and pre-existing Shiite militias that has played a key role in pushing back the jihadists.

The paramilitary umbrella group has vowed to stay out of Mosul proper but on Saturday opened a new front by pushing toward Tal Afar, a town west of Mosul, with the aim of cutting off the city from Syria.

The mawakeb are sometimes described as the civilian branch of the Hashed al-Shaabi.

- Food, clothes and cigarettes -

On their vehicles, Sistani's portrait is everywhere. Some of the volunteers have his picture taped to their clothes or the back of their mobile phones.

"Hashed is as much about fighting as it is about serving the fighters," said Abu Ali al-Akiali, who led the day's convoy to Fishqeh, south of Mosul.

He said the massive delivery operation, which never seems to suffer from the same budgetary turbulence that affects the police and the army, was financed entirely by private donations.

"Day and night, these convoys are there for us," said Ali, a 30-year-old who said he joined the Hashed al-Shaabi on the very day Sistani called for mass mobilisation.

The services provided by the mawakeb are not restricted to members of the Hashed al-Shaabi, an organisation dominated by Iran-backed Shiite militias often accused of sectarianism.

Hussein Ali, a 21-year-old deployed with the federal police in Fishqeh just a handful of kilometres (miles) from the first IS positions, had just received a parcel for his unit.

He listed the day's offerings: "Underwear, shoes, scarves, caps and even mobile phone top-up cards."

"We collect things in our neighbourhoods and bring every fighter some cigarettes, clothes and food," said Mohamed Settar, one of Ali's benefactors.

The engineer and father of two left Baghdad in the middle of the night: "Even a few kilometres from the front line, we're not afraid."

All along the road, snaking through desolate villages recently retaken from the jihadists and dotted with charred car bomb carcasses, residents and fighters waved at the mawakeb, chanting religious slogans and shooting in the air as they drove on to their next delivery spot.