NAIROBI (Reuters) - The economy of the Indian Ocean archipelago of Comoros should grow 3.5 percent this year, up from an estimated 3.3 percent in 2014, helped by public investments and lower fuel prices, the International Monetary Fund said. The economy of the group of four islands between Madagascar and southern Africa relies mainly on agriculture and fishing. In its statement late on Monday, the IMF said the Comoros economy still faces challenges such as high poverty and insufficient infrastructure, and needs to bolster its revenue administration and management of its public finances. "For the medium term, the key challenges are to create fiscal space for infrastructure investment and social spending, accelerate inclusive growth and employment generation, and reduce poverty," the IMF said. "Weaknesses in the business environment, including inadequate infrastructure, especially in the energy sector, and difficulties in contract enforcement represent important challenges," it said. Comoros has been calm in recent years but has had a turbulent history with some 20 coups and attempted coups since declaring independence from France in 1975.