 India, China, Nigeria, Indonesia and the United States are set to lead the world's growth in urban populations during the next four decades, sparking challenges in providing jobs, housing, energy and infrastructure, the United Nations said on Thursday. Ahead of a UN sustainability summit in Rio in June, the world body released new forecasts for urban populations in a bid to urge global leaders to come up with concrete plans at the conference in Brazil to produce sustainable cities. Nigeria's cities are expected to add 200 million people by 2050, more than doubling the country's current population; India's cities are to add 497 million, increasing the current total population by more than 40 percent; and Indonesia's cities are set to add 92 million people, about a 38 percent increase in its total population, according to the UN's 2011 Revision of the World Urbanization Prospects. US cities are forecast to add 103 million people, raising the country's total population by a third, while China is due to boost its total population by a quarter, with an increase of 341 million in its cities. Currently half the world's 7 billion people live in cities, the United Nations said. "Cities are where the pressures of migration, globalization, economic development, social inequality, environmental pollution and climate change are most directly felt," the United Nations said in a statement. "Yet, at the same time, they are they engines of the world economy and centers of innovation where many solutions to global problems are being piloted," the world body said. Representatives from around the world will gather in Rio de Janeiro in June to try to hammer out sustainable development goals at the Rio+20 conference, named after a ground-breaking meeting in the Brazilian city 20 years ago.