A top security expert at the United Nations has warned that the risk that nuclear weapons could be used is at its highest since World War II, calling it an "urgent" issue that the world should take more seriously.

Speaking to reporters in the Swiss city of Geneva on Tuesday, Renata Dwan, director of the UN Institute for Disarmament Research (UNIDIR), said the arms-control landscape was changing - partly due to strategic competition between the United States and China - and noted that all states with nuclear weapons have nuclear modernisation programmes under way, writes Aljazeera.

Traditional arms-control arrangements were also being eroded by the emergence of new types of war, with an increasing prevalence of armed groups and private sector forces and new technologies that blurred the line between offence and defence, Dwan said.

With disarmament talks at a stalemate 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, she said.

"I think that it's genuinely a call to recognise - and this has been somewhat missing in the media coverage of the issues - 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".

The nuclear ban treaty, officially called the Treaty for the Prohibition of Nuclear Weapons, was backed by the International Campaign to Abolish Nuclear Weapons (ICAN), which won the Nobel Peace Prize in 2017.

The treaty has so far gathered 23 of the 50 ratifications that it needs to come into force, including from South Africa, Austria, Thailand, Vietnam and Mexico. It is strongly opposed by the US, Russia and other states with nuclear arms.

Cuba also ratified the treaty in 2018, 56 years after the Cuban missile crisis, a 13-day Cold War face-off between Moscow and Washington that marked the closest the world had ever come to nuclear war.

Dwan said the world should not ignore the danger of nuclear weapons.

"How we think about that, and how we act on that risk and the management of that risk, seems to me a pretty significant and urgent question that isn’t reflected fully in the (UN) Security Council," she said.