According to the UN mission in Iraq's monthly tally, 1,959 Iraqi forces were killed last month and at least 450 others wounded.
The toll includes members of the army, police who are engaged in combat, the Kurdish peshmerga, interior ministry forces and pro-government paramilitaries.
The UN statement also said at least 926 civilians were killed, bringing to 2,885 the number of Iraqis killed in acts of terrorism, violence and armed conflict last month.
"The casualty figures are staggering, with civilians accounting for a significant number of the victims," the top UN envoy in Iraq, Jan Kubis, said.
Kubis said the growing death toll was largely a result of the jihadists' ferocious defence of Mosul, the city where they proclaimed their now crumbling "caliphate" in 2014.
"Daesh (IS) has been employing the most vicious tactics, using civilian homes as firing positions as well as abducting and forcibly moving civilians, effectively using them as human shields," he said.