The UK based rights group, Together Against Genocide (TAG), said it "unreservedly welcomed" the report by the Office of the High Commissioner for Human Rights (OHCHR), and called on the UN Human Rights Council to "take concrete steps and a concrete timeline to deliver successful prosecutions and thus an end to impunity in Sri Lanka."

See full statement here. Reproduced in full below:

Together Against Genocide (TAG) unreservedly welcomes the report of the OHCHR Investigation on Sri Lanka.  We urge the government of Sri Lanka to accept in whole the recommendations of the report.
 
This is a hopeful first step on the long road to justice. Each of the lives lost remains precious to us and we continue to hope to see them fully accounted for and their families granted Justice.
 
We note High Commissioner Zeid’s statement that the government of Sri Lanka, though cordial did not change from former President Rajapaksa’s stance on allowing access to the country to OHCHR investigators.
 
A next step must be for UN investigators to be granted access to the many sites of mass graves and scenes of grave crimes for forensic analysis, as well as to be able to interview witnesses within SriLanka. To-date the majority of witnesses who have been interviewed remain outside of Sri Lanka.
 
We urge the UN Human Rights Council to address the needs of the many survivors who have fled Srilanka and who gave evidence to OISL from international locations in confidence.  A significant proportion of them are stateless. Having bravely come forward to make the OISL possible, they continue to fear for their lives and those of remaining families back home, neither do they feel they can testify safely to SriLankan authorities. They too need justice and to be able to get on with their lives.
 
As noted by High Commissioner Zeid Sri Lanka currently does not have domestic laws recognizing Crimes Against Humanity. Rather than reinventing the wheel. It must accept international standards and ratify the Rome Statute..
 
There remains a huge amount of work to be done and many pitfalls. Survivors of mass atrocities in Sri Lanka have waited too long. We urge the Human Rights Council to now take concrete steps and a concrete timeline to deliver successful prosecutions and thus an end to impunity in SriLanka.