Arusha - Tanzania must find an albino girl kidnapped last month, the country's top UN official said on Friday, expressing "outrage" at a series of attacks on albinos, whose body parts are sold for witchcraft.Kidnappers armed with machetes seized 4-year-old Pendo Emmanuelle Nundi on 27 December from her home in the northern Mwanza region. Police have since arrested 15 people, including the girl's father and two uncles."The government must conduct a full investigation into the matter and arrest the perpetrators," said UN country chief Alvaro Rodriguez on state television, after visiting the worst affected regions in northern Tanzania.Rodriguez urged Tanzania to give the investigation the "highest priority," and promised the help of the UN."We'll do what we can in cooperation with the government to ensure that the girl is brought back," he said.Rodriguez's comments come after he met with albino children whose limbs had been hacked off.At least 74 albinos have been murdered in the east African country since 2000, according to United Nations experts. After a spike in killings in 2009, the government placed youngsters in children's homes in a desperate effort to defend them.A hereditary genetic condition which causes an absence of pigmentation in the skin, hair and eyes, albinism affects one Tanzanian in 1 400, experts say. In the West, it affects just one person in 20 000.In August, a UN rights expert warned that attacks against albinos were on the rise because Tanzania's October 2015 presidential election was on the horizon, encouraging political campaigners to turn to influential sorcerers for support.Albino body parts sell for around $600 in Tanzania, with an entire corpse fetching $75 000.