A U.N. statement quotes envoy Paulo Sergio Pinheiro as saying he found a wireless microphone in the room where he was conducting interviews Saturday in a prison outside Rangoon.
The statement says Burma's government expressed regret when it learned of the incident and gave assurances that it would be fully investigated. The U,N. statement says the government had assured Mr. Pinheiro there would be no interference with his work and that those he interviewed would not be intimidated or punished before, during or after his mission.
Burma's military government has been widely criticized for its human-rights record. Human-rights groups say there are about one-thousand political prisoners in the country.
Mr. Pinheiro arrived in Rangoon last Wednesday for an update on the status of political prisoners. He was also scheduled to discuss allegations of human rights abuses in ethnic minority areas, where the military is accused of using rape as a weapon against minority women.
He is to report his findings to the U.N. Human Rights Commission in three weeks.
The Rangoon government has been the subject of intense criticism for failing to make progress in its reconciliation process with opposition leader Aung San Suu Kyi. Her party won the 1990 elections but was never allowed to take power.
The Pinheiro visit was seen as an important part of efforts to revive the reconciliation process.
In November, Mr. Pinheiro threatened to resign from his position if substantial progress was not made in the political dialogue, the release of political prisoners and plans to allow an independent assessment of human-rights conditions.