SEOUL -- South Korean President Lee Myung-bak on Tuesday stressed the need for close international coordination to strengthen the global nuclear security regime as he opened the plenary session of the two-day nuclear summit.

More than 50 heads of state and representatives of international organizations have gathered here for the Seoul summit, a follow-up to the inaugural Washington summit in 2010 where US President Barak Obama set the goal of securing the world's loose nuclear materials by 2014.

"I expect the Seoul summit, building upon the achievements made at the Washington summit, to take a step further in generating a consensus and action plans," Lee said in opening remarks at the first plenary session of the day.

Noting 1,600 tons of highly enriched uranium and 500 tons of plutonium capable of producing some 126,500 nuclear weapons are stored worldwide, Lee said minimizing and ultimately removing all loose nuclear materials is a fundamental solution for preventing nuclear terrorism. ?

Citing the tsunami-triggered nuclear crisis in Japan last year, the president also said measures meant to enhance both nuclear security and nuclear safety need to be discussed.

"We are all in the same boat, heading in the same direction," Lee said. "We have an obligation to ensure peace, security and happiness for our children and the future generations."

The plenary session will be held for two and a half hours, followed by a working lunch and another plenary session before Lee holds a press conference highlighting the achievements of the two- day summit.