( CNN ) -- Two U.S. Marines died Monday during a `` hostile incident '' in southern Afghanistan , the U.S. military said Tuesday . U.S. Marines walk through a field on patrol on July 13 , 2009 , in Mian Poshteh , Afghanistan . No further details were immediately available in their deaths . `` We deeply mourn the loss of these determined service members , who died in combat defending our freedom and the just cause of Afghans , '' said Brig . Gen. Eric Tremblay , spokesman for NATO 's International Security Assistance Force . `` This is a moment of great sorrow for these members ' families and friends , and I extend my deepest condolences to them during this difficult time . '' The deaths come as almost 4,000 Marines and sailors , along with several hundred Afghan security forces , are working to clear Taliban militants from population centers in the Helmand river valley , in the south of the country . British forces launched a similar offensive in the province in late June . The push , called Operation Khanjar , is targeting militants in Helmand province , a Taliban stronghold and poppy-growing region . The forces are trying to gain and hold ground in the perilous region ahead of national elections this August .
Two Marines killed during a `` hostile incident '' in southern Afghanistan . 4,000 U.S. Marines , sailors working to clear Taliban militants from Helmand river valley . U.S. Marines forces launched a similar offensive in the province in August . Forces are trying to gain ground in the region ahead of national elections in late June .