Japanese cities of Hiroshima and Nagasaki on Tuesday protested against the United States over the nuke power\'s recent plutonium experiment aimed at examining the capabilities of its nuclear weapons. Mayors of the two cities separately sent protest letters to U.S. President Barack Obama, who proposed reducing stockpile of U.S. nuclear weapons by up to one-third two months ago in Berlin. Nagasaki Mayor Tomihisa Taue said in his letter that the test disappointed a lot of people and hurt the sentiment of the bombed places, calling on the United States to stop all nuclear tests and take the initiative in abolishing nuclear weapons. Hiroshima and Nagasaki are the only cities in the world to have been subjected to nuclear attacks and the two cities marked the 68th anniversary of the U.S. nuclear bombing on Aug. 6 and 9 respectively. Hiroshima Governor Hidehiko Yuzaki also sent a protest letter to Obama, saying the U.S. tests have disrupted international efforts to abolish nuclear weapons.