US-led forces have killed more than 36 insurgents in a series of clashes and airstrikes in southern Afghanistan, the coalition said. A militant attack on NATO patrol killed two alliance's troops. Groups of militants began launching attacks Wednesday on a coalition reconnaissance patrol in the south, using rocket-propelled grenades, machine guns and small arms fire, the coalition said Friday. Coalition troops "returned fire with small arms and close air support," destroying several vehicles and killing more than three dozen insurgents, the statement said. Capt. Christian Patterson, a coalition spokesman said Friday night that the operation was still ongoing. He would not disclose the exact location of the clashes. Southern Afghanistan is the center of a six-year-old Taliban-led insurgency in Afghanistan that is gaining strength and spreading to the east. At least 93 US troops have died in the country so far this year, a pace that would make 2008 the deadliest for American forces since the 2001 invasion.