Top officials of Hiroshima and Nagasaki sent letters to the U.S. government Tuesday to protest two rounds of tests on the properties of plutonium, conducted by a federally funded lab last year.
Hiroshima Mayor Kazumi Matsui, Hiroshima Gov. Hidehiko Yuzaki and Nagasaki Mayor Tomihisa Taue lodged written protests with President Barack Obama a day after the National Nuclear Safety Administration announced the lab conducted tests on the so-called Z machine to test the properties of plutonium with X-ray emissions.
The revelation came after the United States conducted a fourth subcritical nuclear test in December. The repeated tests are likely to prompt critics to question the stance of the Obama administration, which has called for nuclear disarmament while maintaining its own atomic stockpiles.
In the letter, Taue noted more than 120 countries recognized the importance of nuclear disarmament at the international Conference on the Humanitarian Impact of Nuclear Weapons, held in Oslo on March 4-5.
Taue also urged Obama to halt all types of experiments relating to nuclear arms and play a leading role in order to wipe out atomic weapons.
In Tokyo, Chief Cabinet Secretary Yoshihide Suga said Japan will not protest the nuclear tests because they did not include a nuclear explosion, which is banned under the Comprehensive Nuclear Test Ban Treaty.
The tests were to "maintain and evaluate the safety and effectiveness" of nuclear weapons, Suga told reporters, adding that Japan will continue to support Obama's vision of a world free from nuclear weapons.
The U.S. tests were conducted at the Sandia National Laboratories in New Mexico.
The United States has continued such plutonium tests to see if its nuclear weapons remain in an operational state. Similar experiments were also carried out in the April-June period of 2012 and at the end of last August.