Mosul battle rages as ISIS bombings across Iraq kill at least 20

Iraq's special forces worked to clear neighbourhoods on the eastern edge of Islamic State-held Mosul on Sunday as bombings launched by the extremist group elsewhere in the country killed at least 20 people.

The Mosul offensive has slowed in recent days as Iraqi forces have pushed into more densely populated areas, where they cannot rely as much on airstrikes and shelling because of the risk posed to civilians, who have been told to stay in their homes.

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"There are a lot of civilians and we are trying to protect them," said Lt. Col. Muhanad al-Timimi. "This is one of the hardest battles that we've faced till now."

Some civilians are fleeing the combat zone, while ISIS militants are holding others back for use as human shields, making it harder for Iraqi commanders on the ground to get approval for requested U.S.-led coalition air strikes. Iraq's special forces are some of the country's best troops, but they still largely rely on air support to clear terrain.

Iraqi forces first entered the eastern edge of the city on Tuesday. On Friday, forces began pushing into Mosul proper, but so far have advanced just over a kilometre into the city.

Twin offensive in Raqqa

They could receive a boost with Sunday's launch of a long-awaited offensive against the ISIS-held city of Raqqa in northern Syria, the de facto capital of the extremist group's self-styled caliphate. That operation, launched by U.S.-backed and Kurdish-led Syrian forces, could force the extremists to split their forces to defend the two largest cities still under their control.

On the southern front of the Mosul battle, Iraqi forces are still some 20 kilometres from the city centre. The fighting is centred on the town of Hamam al-Alil, where Associated Press journalists could hear gunfire and saw attack helicopters firing on ISIS positions.

• Syrian Kurds start offensive to retake Raqqa

Kurdish peshmerga fighters launched mortar rounds and fired heavy artillery at the ISIS-held town of Bashiqa, about 13 kilometres northeast of Mosul. The town, which is believed to be largely empty except for ISIS militants, has been encircled by Kurdish forces.

The extremists captured Mosul and surrounding areas in 2014, and have had plenty of time to dig trenches, block off roads and mine approaches to the city.

"Daesh dug trenches that they filled with water and they have a lot of suicide attackers and car bombs," said al-Timimi, using the Arabic acronym for ISIS.

Series of deadly bombings

The extremists meanwhile struck far from the front lines with a series of bombings.

The deadliest attack took place in the city of Samarra, 95 kilometres north of Baghdad, which is home to a major Shia shrine. Provincial spokesman Ali al-Hamdani said the attacker set off a bomb-packed ambulance in a parking lot near Shiite pilgrims before detonating his explosives vest.

The attack killed 11 people, including at least four Iranians, and wounded up to 100 other people.

Another suicide attacker rammed an explosives-laden car into a busy checkpoint outside the city of Tikrit, killing at least nine people. Al-Hamdani said five female students, a woman and three policemen were killed in the attack, while 25 others were wounded.

ISIS had also captured Tikrit during its lightning blitz across Iraq in the summer of 2014. Iraqi forces drove the militants from the city, around 130 kilometres north of Baghdad, in April 2015.

Iran's Foreign Ministry spokesman, Bahram Ghasemi, condemned the two attacks, which he said had killed 21 people, including 10 Iranian pilgrims, the semi-official Mehr news agency reported. It was not immediately possible to reconcile the conflicting tolls, which are common in the chaotic aftermath of attacks.

In an online statement, ISIS claimed all three bombings and said the ambulance bomb was set off by a second suicide attacker. The AP could not verify the authenticity of the statement, which was posted on a militant website commonly used by the extremists.

In the capital, Baghdad, a series of smaller bombings killed at least 10 people and wounded 21 others, according to police and medical officials, who spoke on condition of anonymity because they were not authorized to brief reporters. No one immediately claimed the attacks, but they bore the hallmarks of ISIS.