By Sherine Tadros, Middle East Correspondent, in Iraq
Ansar Marjaiyeh, or Soldiers Of The Religious Leadership, is a group of Shia volunteers leading the fightback against Islamic State militants near Fallujah.
IS snipers are just 200m away, and they return fire hard and fast. The volunteers are slowly pushing the militants back, but holding the territory they retake is their main challenge.
Their weapons are not impressive, but their resolve is. Dozens of these fighters have been killed so far. This is just one of several open fronts with the Islamic State group in Iraq.
More than 20,000 Shia militiamen from different groups, many backed by Iran, are involved in the fight against IS. They make up what is known as the Popular Mobilisation Force. Around 5,000 Iraqi officers and soldiers are working with them.
The men proudly show off their weapons and what they have picked up during battle.
One militia leader showed us what he said was a receipt, bearing the stamp of the Islamic State group, invoicing the Syrian government for crude oil worth thousands of dollars. The receipt said the oil was to be transferred from Mosul to Syria.
We met up with hundreds of fighters on their way to the frontline in Tikrit - the birthplace of former president Saddam Hussein, which was taken over by IS last summer.
The military operation In Tikrit is in its third week, but the militias still only control parts of the city.
Hadi al Amiri heads up the Badr Brigade, one of Iraq's most effective fighting forces.
Seen by many as Iran's man on the ground, he told Sky News that dozens of Iranian advisors are helping take back territory from IS, and that Tikrit would be retaken within days.
But he insists co-ordination with local Sunni forces has been key, and is confident his men will soon take back Anbar before recapturing the country's second city, Mosul.
He said: "We were victorious in Diyala, and we're using the same strategy here, as a result of a high degree of co-ordination between the army, the popular mobilisation forces and the police."
In Diyala, though, Sunni families returning have found their homes burned and looted. Rights groups say dozens of villages were destroyed not just by IS, but also Shia militias carrying out revenge attacks.
We spoke to people in Diyala who told us they heard about those attacks from their neighbours and friends, but did not see anything themselves.
Militia leaders insist they have strict orders not to harm locals under their control, and near Tikrit, we found Shia fighters helping hundreds of families going home.
There are also some areas where the battle was too fierce, meaning there is nothing left to come back to. Islamic State flags still litter the walls along the streets as mangled metal and charred buildings replace what used to be a vibrant neighbourhood.
For now, the momentum is with the militias and the Iraqi army.
Tikrit will be a strategic and symbolic victory before the push northwards, but that will entail Shia militias controlling Sunni and mixed villages - putting Iraq's delicate sectarian balance to the ultimate test.
