Australia has the tightest security controls among nations with nuclear material while North Korea poses the world's greatest risks, a new index by experts said Wednesday.

The Nuclear Threat Initiative, in a project led by former US senator Sam Nunn and the Economist Intelligence Unit, aims to draw attention to steps that nations can take to ensure the safety of the world's most destructive weapons.

Among 32 nations that possess at least one kilogram of weapons-usable nuclear materials, Australia was ranked as the most secure. It was followed by European nations led by Hungary, the Czech Republic and Switzerland.

On the bottom of the list, North Korea was ranked as the least secure of its nuclear material, edging out Pakistan. The index, which gave rankings on a scale of 100, also listed Iran, Vietnam and India below the 50-point threshold.

"This is not about congratulating some countries and chastising others. We are highlighting the universal responsibility of states to secure the world's most dangerous materials," said Nunn, who has long been active on nuclear safety.

Nunn, a Democrat who represented Georgia in the Senate from 1972 until early 1997, voiced concern that the world had a "perfect storm" -- an ample supply of weapons-usable nuclear materials and terrorists who want them.

"We know that to get the materials they need, terrorists will go where the material is most vulnerable. Global nuclear security is only as strong as the weakest link in the chain," he said.

The index, timed ahead of the March summit on nuclear security in South Korea, called for the world to set benchmarks and to hold nations accountable for nuclear safety.

It also urged nations to stop increasing stocks of weapons-usable material and to make public their security regulations.

North Korea has tested two nuclear bombs and in 2009 renounced a US-backed agreement on denuclearization. The world has watched warily since last month as young Kim Jong-Un takes over as leader from his late father Kim Jong-Il.

Pakistan has vigorously defended its right to nuclear weapons. The father of Pakistan's atomic bomb, Abdul Qadeer Khan, admitted in 2004 that he ran a nuclear black market selling secrets to Iran, Libya and North Korea but later retracted his remarks.

Australia does not have nuclear weapons and supports their abolition. But it has a security alliance with the United States and holds the world's largest reserves of uranium.

Of acknowledged nuclear weapons states, Britain scored best at 10th among the 32 countries. The United States ranked 13th.

The Nuclear Threat Initiative also released a separate index of security conditions in countries without significant nuclear materials, saying they could be used as safe havens or transit points.

Somalia, which is partially under the control of the Al-Qaeda-linked Shebab movement and has effectively lacked a central government for two decades, was ranked last among the 144 countries surveyed.

Other countries that ranked near the bottom included Republic of Congo, Zimbabwe, Eritrea and Chad.

On the top of the list, Finland was ranked as the most secure nation among those without nuclear material. It was followed by Denmark, Spain, Estonia, Slovenia and Romania.