U.N. Secretary-General Ban Ki-moon says that 20 years after the Rwanda genocide, the international community's failure to prevent atrocities in Syria is "a shameful indictment."

The U.N. chief also pointed to "grave and blatant" human rights violations in the Central African Republic, civilians threatened in many regions, and worrying trends such as rising bias against migrants, Muslims, Roma and other minorities in Europe and elsewhere.

Ban spoke at Thursday's New York launch of "Kwibuka 20", a series of events to mark the 20th anniversary of the Rwanda genocide which began hours after a plane carrying the president was mysteriously shot down as it approached the capital, Kigali, on April 6, 1994.

The secretary-general called the genocide "an epic failure" of the international community and said lessons learned must be implemented.