The UN High Commissioner for Human Rights, Louise Arbour, is due in Sri Lanka next week to assess the island's deteriorating rights record, while the UN's top torture investigator, Manfred Novak, is already in the country.
But Human Rights Minister Mahinda Samarasinghe said "neither Novak or Madam Louise Arbour can visit Kilinochchi," the de facto capital of the Liberation Tigers of Tamil Eelam (LTTE).
The minister said the Tigers could use the visit for propaganda and that security was a concern.
"Visiting foreign dignitaries are free to travel to other parts of the country to get a first-hand idea of what's happening on the ground," Samarasinghe told reporters.
Rights groups accuse the government and the LTTE of gross rights abuses, extra-judicial killings and scores of disappearances of civilians and political activists.
Sri Lanka narrowly avoided censure at the United Nations Human Rights Council last month with the UN body putting off a decision to review the island's rights