An Iraqi attack helicopter crashed on Wednesday south of the Mosul battlefield, killing all four crew members, security officials said.
"During an army aviation mission this morning, an aircraft crashed due to a technical failure," the Joint Operations Command coordinating the fight against the Islamic State group said in a statement.
An official in the JOC said the entire crew was killed in the crash.
"The crew of four, two pilots and two technicians, was killed," a captain in Iraq's army aviation told AFP.
"They were heading to Qayyarah on a routine mission," he said, referring to an area that has been the main military hub south of Mosul since the launch on October 17 of an operation to retake the city from IS.
The helicopter was a Russian-made Mi-35 gunship, he said.
He said that the intensity of the war on IS recently meant that the necessary maintenance work on such helicopters was not always satisfactory.
"There is a lot of strain on these aircraft, that have just kept flying lately," the captain said, speaking on condition of anonymity.