The inaugural Nuclear Security Summit to discuss the prevention of nuclear terrorism and the safety of nuclear materials has opened in Washington.

The summit began with a welcome dinner hosted by U.S. President Barack Obama. In attendance were 47 heads of states including President Lee Myung-bak and representatives from the U.N., the International Atomic Energy Agency and the European Union.

During the two-day summit, participants will adopt a joint statement vowing to secure the safety of nuclear materials within four years and a related action plan.

Before the summit's opening, Ukraine pledged to scrap all of its enriched uranium by 2012. Chile also reportedly transferred 18 kilograms of weapons-grade enriched uranium to the U.S. last month.

Apart from the summit, the Russian foreign ministry says it will sign a bilateral agreement with the U.S. on reducing weapons-grade plutonium.