Barack Obama is set to announce a new defence strategy that would reduce the circumstances in which the US would be prepared to use nuclear weapons. It would rule out a nuclear response to attacks on the US involving biological, chemical or conventional weapons. Nor would the US use nuclear arms on non-nuclear states that comply with the nuclear non-proliferation treaty. Mr Obama said he would make exceptions for states deemed in violation of the treaty, naming Iran and North Korea. Ahead of the report's release, Mr Obama told the New York Times he was convinced Iran was on a course that "would provide them with nuclear weapons capabilities". Last week, Mr Obama said he wanted to see new UN sanctions on Tehran "within weeks". Tehran insists its nuclear programme is peaceful, but its refusal to adhere to international demands has raised fears of a possible strike on its nuclear facilities by the US or Israel. Reduction pact The New York Times said Mr Obama described his new policy as "part of a broader effort to edge the world toward making nuclear weapons obsolete, and to create incentives for countries to give up any nuclear ambitions". The details of his plan - the Nuclear Posture Review - are to be published later on Tuesday. Its release comes ahead of a planned signing by Mr Obama and his Russian counterpart, Dmitry Medvedev, of a new nuclear arms reduction pact in Prague on Thursday. The pact, agreed last month, commits Russia and the US to big cuts in nuclear warheads. The pact would replace the 1991 Strategic Arms Reduction Treaty (Start), which expired last December. The new treaty restricts both Russia and the US to 1,550 warheads, about 30% less than currently allowed, the US says. Mr Obama hailed the treaty as the most comprehensive weapons control agreement in nearly two decades. Mr Obama is hosting a nuclear non-proliferation summit in Washington next week, which is set to be attended by dozens of world leaders. The US president has said his goal is to have a nuclear-free world, and has promised to cut the number of nuclear weapons in the US arsenal. A White House statement on Monday said the new nuclear policy offered "an alternative to developing new nuclear weapons, which we reject". Source: BBC