The UN secretary-general, however, welcomed the efforts made by the government of President Maithripala Sirisena, who had come to power on a pledge of reconciliation and reform after defeating Sinhala-strongman Mahinda Rajapaksa in 2015.
Ban welcomed the symbolic steps taken by the government to build bridges among communities, including the decision to sing the national anthem in Sinhala and Tamil on Independence Day in February this year for the first time since the 1950s.
But there was "still much work to be done in order to redress the wrongs of the past and to restore the legitimacy and accountability of key institutions, particularly the judiciary and the security services," the UN chief said.
"More can and should be done to address the legacy of the past and acknowledge the voices of the victims," he said while delivering a lecture on 'Sustaining Peace and Achieving Sustainable Development Goals' here.
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He said this was "critical for reconciliation, and for ensuring respect for human rights of all Sri Lankans, without regard for ethnicity, religion and political affiliation."
The UN chief suggested that the size of the military force in the North and the East could be reduced to help build trust and reduce tension at the same time.
"To recover from the cataclysms of the past, Sri Lankans will need all four elements of post-conflict resolution: truth-telling, accountability, reparations and institutional reform. There is no fast route to achieving this. It will take many years of political courage and determination," he said.
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