The Turkish defense ministry confirmed its military unleashed a barrage of artillery fire and air strikes on Monday afternoon before ground forces entered northern Iraq to "demolish the caves and shelters that are being used by terrorist groups and to eliminate terrorists" — a reference to the outlawed PKK. 

"The operation, with the support of our attack helicopters, is continuing as planned," the statement said further. While cross-border shelling has happened somewhat frequently in the past, Turkey has rarely sent ground troops.

Back in December 2015 when Turkey, claiming to be engaged in counter-ISIS and general counter-insurgency operations, crossed into Iraq with a large ground force then Iraqi Prime Minister Haidar Abadi demanded Turkey cease violating Iraqi sovereignty, in a standoff which proved a major embarrassment for Baghdad.