International experts gathered in Vienna Monday to discuss tightening restrictions on material that could be used for nuclear bombs, with Russia and the United States warning of the danger of nuclear terrorism.
Meeting chairman Alec Baer of Switzerland said delegates would aim to "tear down" the current agreement, known as the Convention on the Physical Protection of Nuclear Material (CPPNN), and rebuild it with a view to preventing attacks using weapons of mass destruction such as nuclear arms.
"We intend to tear it down, because it's inadapted, and build it up again, keeping the roof and the walls, and put it up to the current level of the threats posed by nuclear terrorism," he told a news conference.
Delegates from 91 of the 111 nations which have signed the CPPNN were expected to endorse a series of amendments to the charter to improve the security of nuclear bomb materials, mainly plutonium and uranium, during the four-day conference.
The amendments would seek to better limit and control access to this material, improve transport security, and limit the vulnerability of nuclear reactors to attacks carried out via computer networks.
Meanwhile the foreign ministers of Russia and the United States warned of apocalyptic consequences if weapons of mass destruction were to fall into terrorist hands.
"Terrorists obtaining nuclear, chemical, biological or radiological weapons would mean only one thing: mass death and destruction far exceeding what happened in the US on September 11," Russian Foreign Minister Sergei Lavrov and US Secretary of State Condoleezza Rice wrote in a joint article in the Russian daily Izvestia.
The ministers welcomed their two countries' co-operation in the Proliferation Security Initiative that aims to clamp down on the smuggling of materials used in weapons of mass destruction and encouraged more countries to join.
They cited the case of Abdul Qadeer Khan, a Pakistani nuclear scientist who leaked nuclear secrets to Iran, Libya and North Korea as an example of what criminals could do to obtain WMD.
The International Atomic Energy Agency, which is hosting the CPPNN gathering, has warned that nuclear proliferation coupled with a terrorist threat means there is a real risk of a September 11-style nuclear attack.
Last November, its head Mohamed ElBaradei said that his agency had never assumed until the suicide jet attacks in New York and Washington that terrorists could ever use nuclear or radiological weapons - the latter known as a "dirty bomb."
But those attacks and the growth of an illicit market in fissile materials had left previous assumptions about nuclear security out of date.
"We need to take preventive measures before a nuclear or radiological emergency," he said then.
The director of nuclear security at the IAEA, Anita Nilsson, said the challenge amid the increased global proliferation dangers was to "detect, delay and respond."
"There is no one size fits all. Each country must determine its current threat level to which it thinks itself exposed" and impose appropriate levels of protection, she added.
Nuclear terrorism could involve the theft of fissile material, essentially the uranium and plutonium that are needed to make a nuclear bomb, to the theft of radioactive material for use in a "dirty bomb" where nuclear materials are spread by conventional explosives.
It could also involve sabotaging a nuclear reactor, or vehicles, ships or aircraft using or transporting nuclear material.