A top Australian nuclear disarmament diplomat has welcomed the new United States doctrine limiting the potential use of its nuclear weapons, but says it could have gone further. The US says it will only use atomic weapons in "extreme circumstances", will not attack non-nuclear states and has pledged that no new nuclear weapons will be developed. The former Australian foreign minister and co-chair of the International Commission on Nuclear Non-proliferation and Disarmament, Gareth Evans, says the new US doctrine takes a step in the right direction by ending a long-standing policy of ambiguity and states clear limits to US nuclear...