British troops are patrolling the Kosovo-Serbia border as part of a NATO peacekeeping presence being bolstered amid concern that the former wartime foes could return to open conflict following a series of violent incidents in recent months. The North Atlantic Treaty Organization sent hundreds of additional forces to Kosovo from Britain and Romania after a battle between the authorities and armed Serbs holed up in a monastery turned a quiet village in northern Kosovo into a war zone on Sept. 24. One police officer and three gunmen were killed in the village of Banjska in what was seen as the worst violence since Kosovo declared independence from Serbia in 2008.