* Second nuclear security summit draws Obama, other leaders
* IAEA says progress made, but incidents show more needed
* U.S.-based group warns against "missed opportunity" in Seoul
By Fredrik Dahl
VIENNA, March 21 (Reuters) - More still needs to be done to safeguard nuclear and radioactive materials given the scores of security incidents the U.N. atomic agency hears about each year, a senior official said on Wednesday.
Khammar Mrabit, a director of the U.N. International Atomic Energy Agency, said much had been achieved in the last decade to help make it harder for militants to carry out "malicious acts" involving potentially dangerous nuclear substances.
But, Mrabit told reporters ahead of next week's Nuclear Security Summit in South Korea: "Nuclear security is work in progress. Continuous improvement is a must. Complacency is bad."
"The agency continues to receive reports ... which show that nuclear and other radioactive materials (are) still not properly secured. We have roughly around 200 incidents per year," said Mrabit, who heads the IAEA's Office of Nuclear Security.
He was referring to cases reported to the IAEA's Illicit Trafficking Database by the 113 countries which participate in this information exchange project, covering cases including theft, sabotage, unauthorized access and illegal transfers.
The percentage involving highly enriched uranium, which can provide material for bombs, is "very low," he said, adding most cases concerned other types of radioactive materials.
The Vienna-based body is helping states prevent smuggling of uranium, plutonium or other items that could be used to make a nuclear weapon or a dirty bomb, which combines conventional explosives such as dynamite with radioactive material.
Analysts say radical groups could theoretically build a crude but deadly nuclear device if they have the money, technical know-how and the amount of fissile material needed.
They say groups such as al Qaeda have been trying to get the components for a nuclear bomb. Obtaining weapons-grade material is the biggest challenge and keeping it secure is vital.
In 2010, U.S. President Barack Obama hosted the first global nuclear security summit in Washington, at which he secured specific commitments from world leaders to help keep bomb-grade material out of terrorists' hands.
Independent experts say most of the pledges are being met though many were modest in scope.
The March 26-27 Seoul nuclear security conference, expected to be attended by some 50 world leaders including Obama, is focused on preventing nuclear terrorism and safeguarding nuclear materials and facilities.
"The 2010 summit focused attention and galvanized action to better secure nuclear materials," said Kelsey Davenport, co-author of a report published this month by the U.S.-based Arms Control Association.
"It would be a huge missed opportunity if states do not make significant new commitments and adopt higher nuclear security standards in Seoul to better safeguard vulnerable nuclear material," she said.
The IAEA sees continuous improvement in nuclear security and "this is really good," Mrabit said.
"Many people will hope that the summit will give an additional high-level political impetus to global efforts to improve nuclear security worldwide," he said.
In the last decade, he said, the IAEA has trained more than 10,000 people from 120 countries in different areas of nuclear security. Together with member states, it has also secured thousands of radioactive sources that were vulnerable.
"Through that we have made it more difficult for people to carry out malicious acts," Mrabit said.