China on Sunday has urged the US to drop its "Cold War mentality" after Washington said it planned to diversify its nuclear armoury with smaller bombs.
"The country that owns the world's largest nuclear arsenal, should take the initiative to follow the trend instead of going against it," said China's defence ministry.
The US is concerned about its nuclear arsenal becoming obsolete and no longer an effective deterrent. It names China, Russia, North Korea and Iran as potential threats.
The US military believes its nukes are seen as too big to be used and wants to develop low-yield bombs.
Russia has already condemned the plan, says BBC.
Iran's foreign minister claimed it brought the world "closer to annihilation".