VIENNA  - World leaders are expected to call next week for more action to minimise civilian use of highly-enriched nuclear fuel to help prevent al Qaeda-style militants from obtaining atomic bombs, a draft summit statement shows.

Holding a third nuclear security summit since 2010, in The Hague on March 24-25, leaders from 53 countries - including US President Barack Obama - will say much headway has been made in reducing the risk of nuclear terrorism in the past four years.

But they will also make clear that many challenges remain and stress the need for increased international cooperation to make sure that highly-enriched uranium (HEU), plutonium and other radioactive substances do not fall into the wrong hands.

Analysts say that radical groups could theoretically build a crude but deadly nuclear bomb if they had the money, technical knowledge and fissile materials needed. “This summit focuses on strengthening nuclear security and preventing terrorists, criminals and all other unauthorised actors from acquiring nuclear materials that could be used in nuclear weapons, and other radioactive materials that could be used in radiological dispersal devices,” the draft said. “Achieving this objective remains one of the most important challenges in the years to come.” The text obtained by Reuters was dated from early this year and a few bracketed parts showed changes are still possible.

The Dutch hosts say the aim is a summit communique “containing clear agreements” to prevent nuclear terrorism by reducing stockpiles of hazardous nuclear material, better securing such stocks and intensifying international cooperation.

Referring to a push to use low-enriched uranium (LEU) as fuel in research and other reactor types instead of more proliferation-prone HEU, the draft said: “We encourage states to continue to minimise the use of HEU through the conversion of reactor fuel from HEU to LEU, where technically and economically feasible. “Similarly, we will continue to encourage and support efforts to use non-HEU technologies for the production of radio-isotopes, including financial incentives.” A senior US administration official said the number of countries possessing HEU and plutonium - which she called “the world’s most dangerous materials” - had significantly declined.

“Twelve countries are now HEU-free, and a significant number of former nuclear facilities no longer possess HEU or plutonium,” said Elizabeth Sherwood-Randall, coordinator on defence policy, weapons of mass destruction and arms control.

But much remains to be done: As of late last year, 30 countries had at least 1 kg of HEU in their civilian stocks, including several Western states and others such as Pakistan, Uzbekistan, Kazakhstan and Belarus, the International Panel on Fissile Materials says on its website. Twenty-seven nations still had different types of research and other reactors using HEU, with Russia having the most, the data showed.

A senior UN official last year told Reuters that nuclear and radioactive materials were still going missing and the information the UN atomic agency receives about such incidents may be just the tip of the iceberg.

As in Washington in 2010 and in Seoul in 2012, individual countries or groups of countries are expected to use the meeting to announce more specific measures than those outlined in the summit declaration that must be agreed by all participants.

“While the Dutch hosts tried out some venturesome ideas in early drafts, many were whittled down in later discussions,” Harvard Professor Matthew Bunn said, adding that so-called “gifts” announced by countries would be more interesting.

Obtaining weapons-grade fissile material - HEU or plutonium - poses the biggest challenge for militant groups, so it must be kept secure both at civilian and military sites, experts say.

An apple-sized amount of plutonium in a nuclear device and detonated in a highly populated area could instantly kill or wound hundreds of thousands of people, according to the Nuclear Security Governance Experts Group (NSGEG) lobby group.

But a so-called “dirty bomb” is seen as a more likely threat than an atomic bomb: conventional explosives are used to disperse radiation from a radioactive source, which can be found in hospitals or other places that may not be very well secured.

Mexican police in December found a truck they suspected was stolen by common thieves which carried a radioactive medical material that could have provided such an ingredient.

“High-activity radioactive sources can be used for malicious acts. We have made progress in better protecting sources, inter alia through national registers,” the draft said.

It urged countries that have not already done so to “establish appropriate security plans for the management of spent nuclear fuel and high-level radioactive waste.”