US President Barack Obama's administration has unveiled plans for substantial reductions in America's nuclear weapons' stockpile.
But its strategy review warned Iran and North Korea they would remain potential targets if they continued to defy the international community.
The US also raised concerns about the "lack of transparency" surrounding China's nuclear programme.
It said the US would only used nuclear arms in "extreme circumstances".
For the first time, the US is ruling out a nuclear response to attacks on America involving biological, chemical or conventional weapons.
But the Nuclear Posture Review comes with a major condition: countries will only be spared a US nuclear response if they comply with the Nuclear Non-Proliferation Treaty - this does not include Iran and North Korea.
"[Tehran and Pyongyang's] continued defiance of international norms and agreements will lead only to their further isolation and increasing international pressure," the document notes.
http://news.bbc.co.uk/2/hi/americas/8604217.stm