Obama warns leaders of nuclear terror threat

US President Barack Obama gathered world leaders at a 47-nation summit last night, aiming to deprive terror groups of nuclear weapons and warning of a grave and growing threat to the planet.

Obama will seek firm pledges on securing loose nuclear material in weapons, atomic reactors and stockpiles within four years, as the largest global meeting hosted by a US leader since 1945 opened last night.

Top powers will talk for two days about different aspects of the nuclear threat, focusing especially on stocks of separated plutonium and enriched uranium which could be used by extremists to manufacture weapons.