KABUL, Afghanistan (AP) — Four NATO troops were killed in an insurgent attack Saturday in western Afghanistan, the military alliance said.

NATO did not release the nationalities of the service members killed, or provide a specific location where the attack occurred.

The deaths brought to 24 the number of NATO forces killed this month. At least 2,012 NATO service members have died since the U.S.-led invasion of Afghanistan on Oct. 7, 2001, according to an Associated Press count.

Violence continues unabated in many areas in Afghanistan, with an increase in insurgent attacks and NATO-Afghan operations now gripping the north.

Fighting has also surged in southern Afghanistan since NATO and Afghan forces launched operation Dragon Strike last month in areas around Kandahar city — 260 miles (420 kilometers) southwest of the capital, Kabul — to flush out militants and destroy their strongholds.

Southern Afghanistan is the birthplace of the Taliban, and the hard-line militia’s presence is strong there.

Three NATO service members were killed Friday in the south, including a Briton who died in a roadside blast in Helmand province.