KATHMANDU, Nepal — Rescuers have given up searching for three sherpa guides missing two days after the deadliest ever accident on Nepal's Mount Everest killed at least 13 and shocked the mountaineering world.Snow and huge chunks of ice swept down the perilous and crevasse-riddled Khumbu Icefall on Friday as guides ferried supplies to upper camps for foreign climbers trying to reach the summit of the world's highest mountain.Helicopter searches and teams scouring the area on the ground on Friday and Saturday found no sign of the missing men, who rescuers believe were knocked into crevasses or trapped under snow while preparing the route for climbers."We have called off the search operation. It not possible to find the three missing persons, dead or alive," said Lakpa Sherpa, of the Himalayan Rescue Operation, speaking from base camp, the starting point for Everest expeditions.The helicopters used in the search and to ferry bodies from the mountain have been called back to Kathmandu, an army spokesman said. The official death toll remained 13 fatalities.Rescuers brought six bodies from the base camp to Kathmandu at the weekend and have kept them at a sherpa Buddhist monastery in accordance with tradition. The rest were handed over to families in the Solukhumbu region where the accident took place."The bodies will be carried out from the monastery and cremated separately according to the sherpa tradition on Monday," said Ang Tshering Sherpa of the Nepal Mountaineering Association.Sherpas are an ethnic group in Nepal and have helped foreigners climb the country's towering peaks since before Sherpa Tenzing Norgay and New Zealander Sir Edmund Hilary became the first to reach the top in 1953.