The Nuclear Security Summit, which was aimed at locking down nuclear materials worldwide, ended here on Tuesday afternoon with a communique and a work plan urging for concrete actions and measures.

Leaders from 47 countries, including the hosting United States, and representatives of the United Nations, the European Union and the International Atomic Energy Agency gathered in Washington for the two-day meeting to discuss ways to prevent nuclear materials from falling into the hands of terrorists and "non-state actors."

The communique iterates the participating countries' commitment to the goal of securing nuclear materials in four years, while the work plan lines out specific steps as to how the broad goals and commitments of the communique will be implemented.

"Nuclear terrorism is one of the most challenging threats to international security, and strong nuclear security measures are the most effective means to prevent terrorists, criminals, or other unauthorized actors from acquiring nuclear materials," says the communique.

"In addition to our shared goals of nuclear disarmament, nuclear nonproliferation and peaceful uses of nuclear energy, we also all share the objective of nuclear security. Therefore those gathered here in Washington, D.C. on April 13, 2010 commit to strengthening nuclear security and reducing the threat of nuclear terrorism. Success will require responsible national actions and sustained and effective international cooperation," it says.

"We welcome and join (U.S.) President (Barack) Obama's call to secure all vulnerable nuclear material in four years, as we work together to enhance nuclear security," says the communique.

The work plan says that it "supports the Communique of the Washington Nuclear Security Summit."

"It constitutes a political commitment by the Participating States to carry out, on a voluntary basis, applicable portions of this Work Plan, consistent with respective national laws and international obligations, in all aspects of the storage, use, transportation and disposal of nuclear materials and in preventing non-state actors from obtaining the information required to use such materials for malicious purposes," says the document.

Positive progress was scored at the summit with Ukraine announcing on Monday that it would get rid of its highly enriched uranium within the next two years.

Also on Tuesday, Russia and the United States signed a deal on reducing stocks of weapons-grade plutonium.

U.S. Secretary of State Hillary Clinton and Russia Foreign Minister Sergei Lavrov signed a protocol to a 2000 agreement on eliminating excess weapons-grade plutonium from defense programs.

U.S. officials have said each country is to dispose of 34 metric tons of weapons-grade plutonium by burning it in reactors.

President Obama, addressing a plenary session of the 47-nation nuclear security conference, told fellow leaders on Tuesday morning that it was time "not simply to make pledges, but to make real progress for the security of our people."