Philippines has started drilling for oil in a part of the Spratly Islands also claimed by Vietnam . China says Chinese ships have made violent attacks on Vietnamese vessels . `` It is possible that the Philippines may have been emboldened by the recent defense agreement reached with the United States . Vietnamese fishermen arrested by China authorities in a separate dispute . Situation could escalate into armed conflict , analyst says .
Philippines has started drilling for oil in a part of the Spratly Islands also claimed by Vietnam . China says Chinese ships have made violent attacks on Vietnamese vessels . Vietnamese fishermen arrested by China authorities in a separate dispute . Situation could escalate into armed conflict , analyst says .