BRASILIA (Reuters) -The BRICS group of developing nations is set to announce a new guarantee fund backed by the New Development Bank (NDB) to lower financing costs and boost investment, two people familiar with the matter told Reuters. The initiative, modeled on the World Bank's Multilateral Investment Guarantee Agency (MIGA), aims to address global investment shifts amid uncertainty surrounding U.S. economic policy, the sources said on condition of anonymity. Brazilian officials view the fund as the centerpiece of the BRICS financial agenda during the country's rotating presidency.