Islamic State (IS) militants and fighters from Iraq's Hashed al-Shaabi paramilitary coalition were locked in fierce clashes near Mosul Tuesday, with nearly 30 reported dead, the coalition said.
Mosul, Iraq's second city, was retaken from IS in July after a massive months-long offensive.
"Waad Allah forces are repelling an IS attack southwest of Mosul in the Hatra desert" some 100 kilometres (60 miles) southwest of Mosul, said a spokesman for the Hashed unit.
The Hashed is an umbrella group of paramilitary auxiliaries formed in 2014 to support Iraqi regular forces after IS swept across swathes of northern Iraq.
In a series of online posts, Waad Allah said IS sent "numerous suicide bombers" to attack its forces, and gave a death toll of 24 Islamist militants and four of its own men.
Iraqi forces have retaken more than 90 percent of the territory IS seized in the country in 2014, with the Islamist militants now confined to the desert areas in Anbar province bordering Syria.
But despite a series of stinging defeats, IS in Iraq retains the ability to launch attacks in areas declared "liberated" months previously.
After losing Mosul in July, IS has also just lost Raqa, its "capital" in Syria.
The Hashed took over the Hatra area in April this year after IS forces were ousted.
The ancient walled city of Hatra in northern Nineveh province is on the UNESCO World Heritage List.