Leaders from over 40 countries have started arriving for an unprecedented gathering in Washington for the Nuclear Security summit . <br/><br/>The main objective of the Summit, being held at the initiative of US President Barrrack Obama is to rally collective action behind the goal of securing all vulnerable nuclear materials and preventing nuclear smuggling and terrorism within four years.<br/><br/>The summit will also build on efforts to break black market, detect and intercept nuclear material in transit and use financial tools to disrupt dangerous trade..<br/><br/>Ahead of the summit, the United States said that terrorist groups, including al Qaeda, are not only pursuing the materials to build a nuclear weapon, they also have the intent to use one. <br/><br/>The Deputy National Security Advisor for Strategic Communications Ben Rhodes said that it would be a catastrophic danger to American national security and to global security if they were able to carry out that kind of attack. He also said that there is a substantial amount of vulnerable nuclear material around the world <br/> There will lead two separate plenary sessions; the first focusing on national commitment to secure nuclear material and the second dealing with international conventions that are aimed at strengthening nuclear controls. <br/><br/>Both sessions will focus on the two separated plutonium and highly enriched uranium that can be used to make nuclear explosives. <br/><br/>The attempt will be to deny these fuels to non-state actors to reduce the risk of nuclear terrorism. <br/><br/>Our correspondent says that Prime Minister Dr Manmohan Singh is expected to announce a special initiative by India to help achieve the goal of the summit at the plenary session.<br/>