Kigali, Rwanda - Rwandan President Paul Kagame said on Sunday that the genocide that shattered his country 30 years ago must serve as a lesson against ethnic hatred and indifference.

"Rwanda's tragedy is a warning, as the process of division and extremism, which leads to genocide, can happen anywhere if left unchecked," he said at a commemorative ceremony in Kigali.

The East African nation was mourning the victims of the genocide that killed some 800,000 people as the world, for a long time, simply looked away.

The atrocity began on April 7, 1994, when representatives of the Hutu majority began killing members of the Tutsi minority and moderate Hutus.

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The massacre ended about 100 days later, when the Tutsi Rwandan Patriotic Front (RPF), founded outside the country, invaded from Uganda, with Kagame – now president of Rwanda – at its head.

"Today, our hearts are filled with grief and gratitude in equal measure," Kigali said at the ceremony, which included survivors and high-profile guests like former US President Bill Clinton.

"We remember our dead, and we are also grateful for what Rwanda has become."

"The international community failed all of us, whether by contempt or cowardice," he continued, referring to the late and hesitant response by the United Nations, the former colonial power France and others.

Kagame told a personal story about a relative who had called in vain for rescue in the capital, Kigali, although she had worked for the UN.

UN peacekeepers had turned back at a Hutu militia roadblock not far from her house, Kagame said, but at the same time, had somehow secured the evacuation of international staff and diplomats.

Kagame said all the people in his relatives' house had been killed, with the exception of a niece who was able to escape from the building.