"The Rwandan genocide will haunt the UN and the international community for generations," he remarked after touring the Rwanda Genocide Memorial Centre in Kigali Tuesday at the start of his two day visit.
He said the world was shocked by the 1994 killings, adding that he was in Rwanda to honour the survivors and show the global solidarity with the victims.
"It must never happen again," he said, underlining that the UN has learned profound lessons from the slaughter.
Mr Ki-moon said that the UN member states must protect a population when attacked." Our challenge is to make firm commitment."
"This memorial is a remainder of what a humankind can do," he said, vividly moved by his about one hour tour of the memorial, which displays, among others, some crude weapons such as machetes, bows and spears, knives that were used in butchering approximately 800,000 Tutsis and moderate Hutus.
The memorial also displays recordings of some victims and how they survived the horrific killings, mostly carried out by the notorious Interahamwe militiamen.
The UN Secretary General made a personal contribution of $10,000 towards the survivors' fund.
The tour also included Mr Hassan Jallow, Prosecutor of the International Criminal Tribunal for Rwanda (ICTR), trying the key suspects of the 1994 bloodbath.
The Secretary General is later in the afternoon expected to meet President Paul Kagame before winding up his tour tomorrow.
This is the second visit of Mr Ki-moon to Rwanda. He was in Kigali some two years ago when he was then South Korea's Foreign Minister.
The Former Secretary General, Mr Kofi Annan, visited Kigali in 1998, and admitted that the United Nations had failed in Rwanda during the genocide.
© Hirondelle News Agency