Ravina Shamdasani, spokeswoman for the UN High Commissioner for Human Rights, urged Sri Lankan authorities to "expedite" investigations and prosecute those involved in the crime.
UN records show that there are 5,653 outstanding enforced and involuntary disappearances in Sri Lanka, the statement said.
"We hope that similar progress will be made in uncovering the truth behind the disappearance of several thousand individuals both during and since Sri Lanka’s conflict," Shamdasani said.
Among those missing is a freelance journalist and cartoonist, Prageeth Ekneligoda, who vanished on the eve of the January 2010 presidential election.