US President Barack Obama has called for a top- level summit on nuclear security in Washington in March, officials at the Group of Eight (G8) summit in Italy confirmed Thursday, according to dpa. Obama "used this (G8) opportunity to make a formal announcement of the nuclear security summit to be held in March of 2010," US National Security Council Chief of Staff Mark Lippert told journalists in a briefing issued on Thursday. The US president "believes nuclear terrorism is the most immediate and extreme threat to global security," Lippert said. "He feels the need to help lead an international effort to secure vulnerable nuclear materials within four years, break up black markets, detect and intercept materials in transit, and use financial tools to disrupt the illicit trade in these materials," Lippert said. While the guest list has not yet been decided, Obama is expected to invite between 25 and 30 countries to the summit in Washington in early March. The US president has made the reduction of nuclear arsenals a key plank of his foreign policy, calling in a landmark speech in Prague in April for a world free of nuclear weapons. His administration has highlighted the issues of strategic arms reductions among existing nuclear powers, enforcement of the Non-Proliferation Treaty among non-nuclear powers, and better control of materials which could be used to make nuclear weapons. However, current international and G8 attention is focused on the nuclear programmes in North Korea and Iran, leading to speculation that the spring summit could also deal with those issues. On Wednesday evening, French President Nicolas Sarkozy said that world powers would give Iran until a meeting of Group of 20 (G20) leading economies in the US in September to answer a US offer of direct talks on the Iranian nuclear programme. Simultaneously, G8 leaders issued a joint statement condemning North Korea's recent nuclear and missile tests and urging Iran to cooperate with international nuclear inspectors. The G8 statement said that the group would return to the issue at a meeting of the UN General Assembly in New York, also in September. In a further statement, the G8, four of whose members are nuclear powers (Britain, France, Russia and the US), endorsed Obama's call for a nuclear-free world. "We are all committed to seeking a safer world for all and to creating the conditions for a world without nuclear weapons, in accordance with the goals of the Nuclear Non-Proliferation Treaty," they said. Of the other four G8 members, Germany and Japan strongly oppose nuclear weapons, while Canada and Italy are seen as more neutral on the subject. The leaders also hailed Obama's recent announcement to seek ratification of the Comprehensive Nuclear Test-Ban Treaty. And they welcomed a July 6 agreement between Russia and the US to cut their respective nuclear arsenals by some 20 per cent.