Some nonnuclear nations are expected to call for the outlawing of nuclear arms, a move strongly opposed by nuclear weapons states.
Even as the U.S. State Department last month announced its participation in the conference, a senior U.S. official has made clear the country's opposition to a legal ban on nuclear weapons, saying Washington regards such an approach as ineffective.
The State Department said in November, "this conference is not the appropriate venue for disarmament negotiations or pre-negotiation discussions and the United States will not engage in efforts of that kind in Vienna."
None of the five nuclear weapons states recognized under the NPT, which also include China, France and Russia, sent representatives to the past two meetings on the humanitarian impact of nuclear weapons.
France and Russia have not responded to invitations to the Vienna conference, while Beijing has said it will send a former diplomat who now belongs to a think tank on arms control, according to the Austrian government.
Alexander Kmentt, director of disarmament, arms control and nonproliferation of the Austrian Foreign Ministry, has said he hopes the conference will focus on the dangers to humanity posed by nuclear weapons and provide impetus for stalled disarmament efforts.
Japan's delegation will include Toshio Sano, the Geneva-based envoy for disarmament, and Terumi Tanaka, an 82-year-old secretary general of the Japan Confederation of A- and H-Bomb Sufferers Organizations, the largest group for victims of the 1945 U.S. atomic bombings of Hiroshima and Nagasaki.
"I plan to convey the terrible human casualties caused by the atomic bomb and to call on (nuclear weapons states) to abandon their policy to keep nuclear arms," Tanaka said.
Previous conferences were held in Oslo, Norway, in March 2013, and Nayarit, Mexico, in February this year. In the second meeting, the chair's summary called for efforts toward a treaty outlawing nuclear weapons ahead of the 70th anniversary of the 1945 atomic bombings next year.