U.S. President Barack Obama on Monday evening welcomed world leaders to a working dinner in Washington, kicking off a summit aimed at preventing terrorists from obtaining nuclear weapons.

A soldier checks the vehicle outside the Washington Convention Center prior to the Nuclear Security Summit in Washington, capital of the United States, April 12, 2010. [Zhang Jun/Xinhua]

After a ceremonial welcome at the Washington Convention Center that saw leaders arrive separately and be greeted by Obama, the working dinner went underway, and leaders are likely to focus their discussion on the threat of nuclear terrorism during the dinner.

Before the meeting officially went underway, Obama conducted a series of bilateral meetings with leaders participating in the summit, and he secured some solid support.

In the meeting with Obama, Ukrainian President Victor Yanukovich pledged to get rid of the country's stockpile of highly enriched uranium by 2012, and the United States has agreed to provide technical and financial assistance in that endeavor.

The United States has invited 46 countries to participate in the summit, many of them sending their heads of state or government. The summit is aimed at securing loose nuclear materials around the world in four years, and a joint communique and a specific work plan is likely to be released after Tuesday's two plenary sessions.