Battles rage around Iraqi city of Tikrit

Iraqi troops backed by allied militias continued Tueday to battle so called Islamic State militants on the second day of a large-scale military operation to recapture the town of Tikrit, but their offensive to retake Saddam Hussein's hometown was slowed by roadside bombs, local officials said. 

Fierce clashes were underway mainly outside the town of al-Dour, south of Tikrit, while government troops were shelling militant bases inside the city. 

The battle for Tikrit is the first in a series of campaigns to try to reclaim large parts of northern Iraq from the group.

Capturing the city will help Iraqi forces secure a major supply link for any future operation to retake Mosul, Iraq's second-largest city which has been under militant rule since June. 

State-run Al-Iraqiya television said that forces were attacking from different directions, backed by artillery and airstrikes by Iraqi fighter jets. It said the militants were dislodged from some areas outside the city, but several hours into the operation, it gave no additional details. 

Military operations must be conducted with the utmost care to avoid civilian casualties - UN special envoy

Tikrit, the provincial capital of Salauhddin province, 80 miles (130 kilometers) north of Baghdad, fell to IS last summer, along with Mosul and other areas in the country's heartland. 

US military officials have said a coordinated military mission to retake Mosul will likely begin in April or May and involve up to 25,000 Iraqi troops. But the Americans have said that if the Iraqis aren't ready, the offensive could be delayed. 

READ MORE: Iraqi government forces and militias begin Tikrit offensive

The US led coalition was not involved in the Tikrit operation, Iraqi officials said. A Pentagon spokesman, Steve Warren, said the US was alerted to the offensive before it started but was not asked to provide air power.  

"Right now we are not providing any air power to support the Iraqi operation in the city of Tikrit," Warren told reporters in Washington. "We did note the Iraqi government's statements that they are emphasising minimisation of collateral damage, and we are continuing to monitor it." 

Iraqi forces apparently have the help of Iranian Gen. Ghasem Soleimani, the commander of the Revolutionary Guard's Quds Force, who arrived two days ago, the Iranian semi-official Fars news agency reported. 

The general has emerged as the chief tactician in Iraq's fight against the militants, working on the front lines alongside dozens of advisers from his country's Revolutionary Guard.

Fars also reported drones were flying over Tikrit, without identifying whether they were Iranian or Iraqi. 

The military commander of Salahuddin region, Gen. Abdul-Wahab al-Saadi, told state TV fighting was taking place outside Tikrit mainly on its eastern side.

"Until this moment we have not entered the city," al-Saadi said. "God willing, we will enter, but we need some time as planned." 

Tikrit is an important test case for Iraq's government, which is trying to reassert authority over the divided country. Islamic State fighters have a strong presence in the city and are expected to put up fierce resistance. 

RELATED: Iraqi Shia militia issues list of Sunni IS 'collaborators'

Past attempts to retake Tikrit have failed, as Iraq struggles with its armed forces, which collapsed in the wake of the Islamic State group's offensive last summer.

The offensive comes as momentum has begun to shift since Iraqi soldiers, backed by airstrikes from the US-led coalition, took back the nearby refinery town of Beiji in November. Any operation to take Mosul would require Iraq to seize Tikrit first because of its strategic location for military enforcements.

I call upon those who have been misled to lay down arms and join their people in order to liberate their cities - Prime Minister Haider al-Abadi

Humanitarian Concern

Hours after the offensive began, the UN special envoy in Iraq appealed to warring groups to avoid attacking civilians.

"Military operations reinforced by international and Iraqi air support must be conducted with the utmost care to avoid civilian casualties, and with full respect for fundamental human rights principles and humanitarian law," Nickolay Mladenov said in a statement.

Hadi al-Ameri, the Popular Mobilisation units' powerful commander, on Saturday urged Tikrit residents to leave their homes within 48 hours.

Abadi urged the security forces to spare civilians, a message echoed by the UN and responding to the fears of reprisals.

Civilian's fears

Media reports from Iraq suggest that many civilians are fearful that they may be "punished for the crimes" of IS fighters.

Ghanim Al-Ajeeli, a Sunni tribal sheikh from the Albu Ajeel village north of Tikrit, which has up to 20,000 residents, said he feared being held responsible for the actions of IS.

"We are very concerned by this operation," he told IRIN. "The [Shia] militias will eliminate the entire tribe of Albu Ajeel. They won’t leave a single house,."

He added that families were fleeing to the Tuz district ahead of the assault reaching the area.

Ahead of the operation, Prime Minister Haider al-Abadi called on Sunni tribal fighters to abandon the Islamic State extremist group, offering what he described as "the last chance" and promising them a pardon.

"I call upon those who have been misled or committed a mistake to lay down arms and join their people and security forces in order to liberate their cities," al-Abadi said Sunday during a news conference in Samarra.

His comments appeared to be targeting former members of Iraq's outlawed Baath party, loyalists to Saddam, who joined the Islamic State group during its offensive, as well as other Sunnis who were dissatisfied with Baghdad's Shia-led government.  

A HRW report released in February documented Shia militias taking revenge on civilians they deemed to have been favourable to IS.