Less than a week before global leaders meet in Washington for a summit on stopping the spread of nuclear arms, the US president has unveiled his nuclear doctrine.

Barack Obama's Nuclear Posture Review outlines a sharp decline in the United States' nuclear arsenal, and rules out the use of atomic weapons against non-nuclear armed countries.

However, it stops short of a declaration that the US will not use nuclear weapons first in any conflict.

As Al Jazeera's Rosiland Jordan reports, the review also comes with a stern message for North Korea and Iran.