During a visit to Nagasaki, one of the two Japanese cities hit by US atom bombs in World War II, on Wednesday, Aug 4, Ban Ki-moon pledged solidarity with the citizens of Nagasaki.
He met elderly survivors, known as 'hibakusha', at the ground zero site of the blast.
"The only way to ensure that nuclear weapons will never again be used is to eliminate them all," said Ban Ki-moon.
"I have come to honour the hibakusha for the extraordinary hardships they have had to endure," he added.
On Friday, Aug 6, Ban will attend the anniversary ceremony commemorating the August 6, 1945 atom bomb attack on Hiroshima, which was followed three days later by the Nagasaki bombing.
He will become the first UN chief to attend the Hiroshima anniversary ceremony. Representatives from more than 70 nations are expected in Hiroshima.