United Nations special envoy on human rights in Burma, Paulo Sergio Pinheiro, has arrived in the country at the invitation of the military government.
The diplomat is on a mission to investigate alleged human rights abuses during September's crackdown on democracy protests.
The UN diplomat has been barred from visiting Burma since 2003.
Pinheiro's visit is expected to last through Thursday. However, after receiving initial permission for the visit last month, he said if Burmese officials do not give him full cooperation, he will immediately leave the country.
Last Tuesday, the government rejected visiting UN special envoy Ibrahim Gambari's call for UN-brokered talks with opposition groups.
Detained opposition leader Aung San Suu Kyi has said in a statement that she is ready to cooperate with the military in a dialogue and welcomes United Nations mediation efforts.
The rights group Amnesty International has called on Burma's government to cooperate with Pinheiro and criticized what it called the government's "grave human rights violations."
Information for this report is provided by AP and Reuters.