IS has dug extensive networks of tunnels and stashed them with rations, solar cells for 'charging devices'
The 24-hour Islamic State assault on the Iraqi city of Kirku has ended, with all all IS fighters killed by Iraqi forces or having died in suicide bombings, the city's police chief said.
"Forty-eight Daesh (IS) terrorists have been killed in the clashes," Brigadier General Khattab Omar Aref told AFP, adding that some of them blew themselves up when the security forces cornered them.
The IS assault on Kirkuk, some 175 kilometers (109 miles) south east of Mosul began early Friday in an apparent attempt to draw Iraqi forces away from the group's last major stronghold in the country.
Earlier in the day another 46 people were killed by IS fighters in the city, mostly security forces.
"We have 46 dead and 133 wounded, most of them members of the security services, as result of the clashes with Daesh (IS)," an interior ministry brigadier general told AFP.
A source at the Kirkuk health directorate confirmed the toll as the directorte called for blood donations to assist with the emergency.
The jihadist group has executed hundreds of men and boys over the past few days as Iraqi coalition forces close in on Mosul and heavy skirmishes have broken out in the surrounding areas.
Some 284 men and boys were killed Thursday and Friday after being rounded up from around the city for use as human shields against coalition attacks, a security source told CNN.
The source said corpses were pushed into mass graves at Mosul's now-inoperative College of Agriculture in the north of the city, where the executions took place.
The source said the victims, which included some children, were shot. CNN said it could not independently verify the claim.
The United Nations earlier said that it was "gravely worried" that IS had taken some 550 families from a village nearby Mosul and was using them as human shields.
The casualty count comes as US Defense Secretary Ashton Carter arrived in Baghdad Saturday to review the six-day-old offensive to retake Mosul.
He will meet commanders from the 60-nation coalition which is led by the United States and assists Iraqi forces in their drive against the jihadists.
A senior defense official told reporters ahead of the trip that "It's the beginning of the campaign. We do feel positively about how things have started off, particularly with the complicated nature of this operation."
Carter is also due to meet Iraqi Prime Minister Haider al-Abadi and is expected to discuss Baghdad's objections to Turkish involvement in the Mosul operations.
The long-awaited offensive on the jihadists' last stronghold in Iraq was launched last week, with some 30,000 troops involved in the country's largest military operation since the pullout of US troops in 2011.
Forces have already retaken dozens of villages, mostly south and east of Mosul.
But officials have said the battle for Iraq's second-largest city could take "months". The areas leading into the city have been peppered with landmines and the group has planted suicide vehicles in several locations to hamper the troop's approach.
In another attempt to slow the advance on Mosul, IS has ignited sulfur stores at an industrial plant south of the city, the Wall Street Journal reports.
Col. John Dorrian, spokesman for the U.S.-led coalition in Iraq, said in a statement that “Daesh ignited toxic sulfur residue stored at al-Mishraq (south of Mosul) in an attempt to disrupt the ISF advance.”
An Iraqi general told AFP that the sulfur cloud from plant has killed two civilians.
"Daesh blew up the sulphur plant two days ago and that has led to the deaths of two people among the civilians in nearby villages," General Qusay Hamid Kadhem said.
US troops have been wearing gas masks as the putrid smoke drifts towards a U.S. military base and nearby villages.
The group has dug an extensive network of tunnels in preparation for a long battle, stashing canned foods, clothing, and water in bunkers they could use to take shelter from air strikes or ambush coalition forces.
IS fortifications were discovered in the village of Sheikh Amir, which was re-taken by Kurdish forces on Monday.
Iraqi forces also discovered documents left behind by IS fighters, including a list of orders to be carried out in preparation for sieges, CNN reports.
Among some 12 orders listed were instructions to stockpile at least a month's worth of rations; to avoid gathering in the open in order to avoid attracting airstrikes; and to equip each station with "a solar cell for charging devices."
The jihadists are expected to use hit-and-run tactics, ambushes, snipers, bombs, berms and trenches to slow down and bleed Iraqi forces as they tighten their grip on the city.
Mosul was seized by the so-called Islamic State in 2014 and is at least five times bigger than any other city controlled by the group.
It is the last major population center in Iraq still held by the jihadists, the liberation of which would effectively eliminate the group's self-declared "Islamic caliphate" from Iraq.
(Staff with agencies)