US President Barack Obama says he will substantially narrow the conditions under which the US would use nuclear weapons.

During an interview with the New York Times, Obama promised that the United States would not use nuclear weapons against non-nuclear states which comply with the Nuclear Non-Proliferation Treaty. It is Washington's first explicit promise on the issue. 

The announcement eliminates the calculated ambiguity in the US nuclear position since the Cold War. But Obama also says countries that have violated or renounced the treaty, such as Iran and the DPRK, are not included in his promise.

He says the US may also revise its commitment if there is a biological weapons attack or if a country's development or proliferation of bio-weapons poses a risk of an attack.