Fourteen civil society organizations and 39 activists make the allegation in a statement that commends the report issued by the UNHRC last week.
The statement lauds the many positive contents in the speech made to the UNHRC session in Geneva by foreign affairs minister Mangala Samaraweera, including steps to annul the PTA and the inclusion of offensive remarks and forced disappearances in the penal code.
Lawyer Sudarshana Gunawardena of Rights Now, a signatory to the statement, has told BBC the situation has improved since the new government took over.
However, witnesses were reluctant to come forward as the protection of victims and witnesses is not properly in place, he said.
He argued it was not possible to change overnight something that has been there for a long time, and noted there has not been sufficient changes in the activities of the armed forces.
The statement requests the government to give a speedy political solution to the national question through a meaningful devolution of power.