Experts differ on whether this week's Nuclear Security Summit represented a step forward or whether it amounted to all talk and no action.

The summit was held here on Monday and Tuesday in a bid to figure out how to start securing vulnerable nuclear material worldwide, prevent nuclear smuggling, foil attempts at nuclear terrorism and demonstrate commitment to the issue.

The meeting's participants agreed on several broad points, the first being that the threat of nuclear terrorism was indeed a serious one.

Participants also agreed to secure vulnerable nuclear materials within their borders in four years' time, which was the goal U.S. President Barack Obama outlined in a speech in the Czech capital Prague one year ago. They also agreed on what Obama called the responsibility of nations to "maintain effective security of the nuclear materials and facilities under our control."

Leaders also committed to what Obama called a sustained program of international security.

But one point stoked controversy among some experts: The U.S. president said no new institutions were needed, but that the summit aimed to strengthen those that already exist, such as the United Nations and the International Atomic Energy Agency (IAEA).

"By primarily endorsing existing instruments ...the summit has missed the opportunity to affirm that protection of weapon-usable materials from theft is an international responsibility and is too important to be left up to the individual states to implement as they see fit," said Edwin Lyman, senior scientist at the Union of Concerned Scientists.

He added that while the summit achieved what he called a few important but minor objectives, it was a major disappointment.

"What is needed, and what the summit should have endorsed but didn't, is a new international regime with stringent mandatory standards, formal peer reviews and tough enforcement mechanisms," he said.

The summit also failed to address the continued production and stockpiling of plutonium in certain countries, he added.

"As stocks of vulnerable materials grow, they will be even harder to secure than they are today, making an already dangerous situation seem worse," he said.

U.S. regulations for protecting this material from theft when it is transferred to the civilian nuclear sector are completely inadequate, he said.