The UN Secretary General, who is on the final leg of his two-day official visit to the island nation, visited former war-torn Jaffna on Friday where he visited a resettlement site and met with displaced people.
Just before his arrival, hundreds of people had lined outside the Jaffna Library, holding placards and pictures of those missing.
Sri Lanka faced a 30-year civil conflict between government troops and Tamil Tiger rebels which ended in May 2009 with the defeat of the rebels.
Thousands of people have been listed as missing in the final stages of the war and the families have continuously called for an international probe.
Ban, earlier in the day, told a gathering in Colombo that while Sri Lanka had made progress, 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 judiciary and security services.
He also urged the government to speed up the return of land so that the remaining communities of displaced people can return home.
