Insurgents killed three British soldiers patrolling in southern Afghanistan on Tuesday, a day after NATO took command of the insurgency-wracked region, officials said. A fourth soldier was seriously wounded. The British military initially reported that two soldiers had been killed and a third unaccounted for but presumed dead following the ambush in volatile Helmand province. Lt. Col. Kevin Stratford Wright, spokesman for the British Helmand Task Force, later confirmed that the missing soldier had been killed. A fourth was seriously wounded and evacuated to a military hospital in Helmand.