NIAMEY (Reuters) - A leader of Niger's Tuareg-led rebel movement was killed when government troops backed by helicopters captured a rebel position in the north of the West African state, a government army officer said on Saturday. Niger's defence ministry had announced on Friday the recapture by the army of Tazerzait, at the foot of Mount Tamgak in the Agadez region, a position which Niger Justice Movement (MNJ) fighters had attacked and taken a year ago.