RIO DE JANEIRO – The United Nations' largest-ever conference has kicked off in Rio de Janeiro.
The Rio+20 conference on sustainable development is expected to draw some 50,000 participants including delegates, environmental activists, business leaders and indigenous groups.
The event runs through June 22, with three final days of high-profile talks among some 130 top leaders from nations around the globe.
Secretary of State Hilary Clinton is heading the United States' delegation. President Barack Obama is not expected to attend.
Brazilian President Dilma Rousseff was on hand for Wednesday's inauguration at the massive conference center in a Rio suburb where the event is centered.
Rio+20 is a follow-up on an environmental summit held in Rio in 1992.
Sustainable development aims to find less environmentally healthy ways of reaching economic growth.