Iraqi warplanes and artillery began pounding Tikrit this morning as 30,000 troops and irregulars prepared to attack the city, a stronghold of the Islamic State insurgency. The operation in the birthplace of former dictator Saddam Hussein was announced last night by Iraq's prime minister, who urged soldiers and government-backed Shiite militias to spare civilians. Speaking from Samarra, the other main city in Salaheddin province, Haider al-Abadi appeared to be addressing fears of reprisals against the Tikrit area's mainly Sunni population. Scroll down for video . Attack: Volunteer Shiite fighters, who are supporting the Iraqi government forces in the fight against the Islamic State group fire a howitzer artillery canon in the village of Awaynat near the city of Tikrit . Irregulars: Iraqi security forces and Shi'ite fighters chant slogans as they gather at Udhaim dam, north of Baghdad, ahead of an advance on Islamic State positions Tikrit that is expected to begin today . Feeding the soul: Soldiers and irregulars take a moment to pray as Iraq masses its forces outside the city, which was the birthplace of Saddam Hussein and an important step on the road to the IS-held city of Mosul . Feeding the body: Fighters scoff their rations ahead of the attack. It is feared the mainly Shiite forces of the Iraqi government could attack the area's mainly Sunni population, worsening sectarian divisions . On social media, Mr Abadi called 'for utmost care in protecting civilian lives and property' in the city, which was last year the scene of a brutal massacre of hundreds of mainly Shiite Iraqi army recruits. Government forces have been working their way north in recent months, notching up key victories against IS. But Tikrit, which has resisted them several times, is their toughest target yet. 'Security forces are advancing on three main fronts towards Tikrit, Ad-Dawr (to the south) and Al-Alam (to the north),' a senior army officer on the ground told AFP by telephone. The army officer said the forces involved in the battle were from the army, police, counter-terrorism units, a government-controlled volunteer group known as the Popular Mobilisation units and local Sunni tribes opposed to IS. 'The attack is being carried out using fighter jets, helicopters and artillery targeting Tikrit to secure the advance and cut supply routes,' he said. Military sources said Iraqi warplanes were involved but it was not immediately clear whether foreign air support - Iranian or from the US-led coalition fighting IS - was also called in. According to both Iraqi and Iranian media, Qassem Suleimani - supremo of the elite Iranian Quds force, specialising in 'subversive warfare' - was in Salaheddin province to help coordinate operations. Massing: Iraqi Army and volunteer fighters prepare at Sedull Udeyim region before moving into Tikrit . Good morale: Iraqi forces have notched up key victories against IS as they've inched north in recent weeks . Religion: A soldier walks past a line of armoured cars, one of which has a photo of a cleric in the window . Cavalry: Iraqi armoured personnel carriers are lined up ahead of the attack on Tikrit today . Tikrit would be the biggest victory yet for Iraqi forces battling Islamic State, but the attack by thousands of Shiite irregulars could severely test the government's ability to handle sectarian divisions. Iraq is bitterly split between minority Sunnis, who were an important base of support for Saddam Hussein, despite his regime's nominal secularism, and the Shiite majority. Since the Islamic State insurgency began, the Iraqi military is heavily dependent on Shiite militias that have been accused of abusing Sunni communities elsewhere in Iraq. 'The priority we gave to the armed forces and all the forces taking part alongside them is to preserve the security of citizens,' Mr Abadi said last night. Hadi al-Ameri, the Popular Mobilisation commander, appealed to Tikrit residents on Saturday to leave their homes within 48 hours so government forces could 'wrap up the battle of the revenge for Speicher.' Speicher is a military base near Tikrit from which hundreds of new, mostly Shiite, recruits were kidnapped before being executed last summer, as the Islamic State insurgency took control of much of Iraq's Sunni Arab heartland. Shiite militias in particular have vowed to avenge the Speicher executions, sparking fears of mass killings against Sunnis if Tikrit were to be recaptured. Mr Abadi appealed to residents to turn against the jihadists, who have suffered a string of military losses since a U.S.-led coalition of Western and Arab nations stepped up their support for Iraq's embattled government. 'I call on all those who were misled and made mistakes in the past to lay down their arms today. This may be the last chance,' Mr Abadi said, suggesting some could be granted amnesty. Iraqi forces tried and failed several times to wrest back Tikrit, a Sunni Arab city on the Tigris river around 100 miles north of Baghdad. Ready: A wide view shows Iraqi soldiers and Shiite irregulars massing at the Udhaim dam. Tikrit would be the biggest victory yet for Iraqi forces battling Islamic State . Taking a moment: An Iraqi soldier rests on a wall at the Udhaim dam. An army officer said the forces involved in the battle were from the army, police, counter-terrorism units, volunteer units and local tribes . Armed: Troops wander the streets around Udhaim dam while they wait for the order to attack. The arrival of many thousands of Shiite fighters in the mainly Sunni city of Tikrit risks inflaming sectarian divisions . Last phone call? A soldier chats on his mobile phone as columns of vehicles move past on their way to attack . The military commander for Salaheddin province, Abdel Wahab Saadi, said Tikrit had both symbolic and strategic importance. 'The aim of course is to liberate Salaheddin to allow for the return of displaced families but it is also going to be a stepping stone on the way to liberating Mosul,' he told AFP. Tikrit is the hometown of executed dictator Saddam Hussein, the remnants of whose Baath party have collaborated with IS in attempting to topple the Shiite-dominated government. IS declared a 'caliphate' last June straddling Iraq and Syria, where the US-led coalition has also been conducting air strikes but not coordinating with any significant ground force.
Artillery and warplanes began pounding Tikrit this morning ahead of attack . The city north of Baghdad is a stronghold of the Islamic State insurgency . Iraqi Prime Minister Haider al-Abadi calls on troops to spare civilians . Tikrit was the scene of a massacre of mainly Shiite army recruits last year .