A three-member team of the United Nations Working Group on Enforced or Involuntary Disappearances, wrapping up its 10- day official visit to the island, said it had found an illegal detention centre in the eastern district of Trincomalee where people had been tortured.
The secret 12-cell prison had markings on the walls that indicated detainees were kept there till 2010 - one year after the nearly three-decade-long war against the LTTE ended, the group said.
"We believe it's an important discovery and it should be properly investigated," he said, adding that "interrogation and torture took place" inside underground cells at the centre.
The experts urged the Sri Lankan government tomeet the rights and legitimate expectations of thousands of families of the disappeared.
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"The widespread use of enforced disappearances for many decades has left profound wounds in the society and a deep sense of mistrust among the relatives," stressed the Group's Vice-Chair Bernard Duhaime, Tae-Ung Baik, and Dulitzky.
The delegation travelled through Sri Lanka's former war zones and met top officials and rights activists besides ethnic minority Tamil families whose kin had disappeared in the civil war.
They said they met hundreds of relatives of disappeared and missing persons throughout the country, "hearing many tragic and deeply saddening stories".
The team visited - in addition to Colombo - Galle in the south, Jaffna, Kilinochchi, Mannar and Mullaitivu in the north and Trincomalee and Batticaloa in the east.
They met with President Maithripala Sirisena, Prime Minister Ranil Wickremesinghe and Minister of Foreign Affairs Mangala Samaraweera as well as other high-level officials.