The first meeting under a UN treaty to ban nuclear weapons will take place next week in Austria. But Japanese representatives will not be there, even as observers.
NHK World spoke with a government official about the decision, which has angered Japan's atomic bomb survivors.
The Treaty on the Prohibition of Nuclear Weapons, or TPNW, was adopted in 2017 and entered into force last year. It is the first international agreement to make the weapons illegal.
The world's nuclear-armed states have not signed the treaty, however. Others that rely on the so-called "nuclear umbrella" for deterrence, including Japan, have not joined either.
On Wednesday, Japan announced it would not send a representative to the meeting. That is despite repeated calls from hibakusha, or atomic bomb survivors, to attend.
In an interview with NHK World, a Foreign Ministry official says the government is focusing on what he called "realistic approaches" on disarmament.
Ishii Yoshizane from the ministry's Arms Control and Disarmament Division said, "We have to remember that to achieve a world without nuclear weapons, we will need the cooperation and involvement of nuclear weapons states.'' He noted that ''none of these nuclear weapon states'' are party to the TPNW.
Ishii said Japan is encouraging countries to ratify other treaties to achieve a nuclear-free world. They include bans on nuclear testing and materials.
Ishii said, "We want to insert efforts so that those such efforts make a meaningful advancement, and that is where we want to be. That has to be based on the confidence and trust that we have with our ally with the United States."
Japan's government says it will send a representative to a separate event in Vienna next week.
The Austrian government will host a conference on the Humanitarian Impact of Nuclear Weapons.