In the lead-up to the last Nuclear Non-Proliferation Treaty (NPT) review conference in 2010, the world was buoyed by U.S. President Barack Obama's pledge to seek a nuclear-free world, but five years on hopes have been dashed that atomic arms will be abolished anytime soon, the U.N. disarmament head said.

"Since the 2010 last review conference, the world has changed," Angela Kane, the high representative for disarmament affairs, said in an interview ahead of the once-every-five-years conference that kicks off Monday.

Citing a host of political and humanitarian crises that have taken root in the Middle East, Ukraine and elsewhere since then, she said she believes top leaders and disarmament experts will face a difficult time during the more than three-week-long conference.