Tehran is the country's capital and largest city, as well as its leading cultural and economic center. Iran is a major regional and middle power, exerting considerable influence in international energy security and the world economy through its large reserves of fossil fuels, which include the largest natural gas supply in the world and the fourth-largest proven oil reserves. Iran's rich cultural legacy is reflected in part by its 19 UNESCO World Heritage Sites, the fourth-largest number in Asia and 12th-largest in the world.