Risk of nuclear war 'highest since WWII'

The risk of nuclear weapons being used is at its highest since World War II, a senior UN security expert says.

UN Institute for Disarmament Research director Renata Dwan has called it an urgent issue that the world should take more seriously.

All states with nuclear weapons have nuclear modernisation programs under way, she said, adding that the arms control landscape is changing, partly due to strategic competition between China and the US.

Traditional arms control arrangements are also being eroded by the emergence of new types of war.

There is an increasing prevalence of armed groups and private sector forces, and new technologies that blur the line between offence and defence, Dwan told reporters in Geneva on Wednesday.

With disarmament talks stalemated for the past two decades, 122 countries have signed a treaty to ban nuclear weapons, partly out of frustration and partly out of a recognition of the risks.

"I think that it's genuinely a call to recognise ... that the risks of nuclear war are particularly high now, and the risks of the use of nuclear weapons, for some of the factors I pointed out, are higher now than at any time since World War II," Dwan said.

On Wednesday, China's disarmament ambassador in Geneva accused Washington of sabotaging and tearing up deals, having a "Cold War mentality" and displaying bullying behaviour.