Burma has been widely condemned for its use of forced labour
A United Nations human rights envoy has decided to leave Burma early after finding a hidden microphone in a room where he was meeting political prisoners.
The Brazilian envoy, Paulo Sergio Pinheiro, said
he would leave Rangoon on Monday, two days ahead of
Mr Pinheiro found the microphone on Saturday, while talking to prisoners inside Insien jail on the outskirts of Rangoon, a UN statement said.
Correspondents say this incident will be very embarrassing for the Burmese military authorities, who had promised the envoy he could go anywhere he wanted and interview anyone he chose in absolute privacy.
Burma already faces international criticism for its poor human rights record.
Human rights groups say about 1,000 political detainees remain in prisons around Burma.
Mr Pinheiro was visiting Rangoon for his fifth visit
to monitor the condition of the country's political prisoners.
He is due to deliver a report on the situation to the UN Human Rights Commission in Geneva at the end of the month.
When he found the microphone - said to date back to World War II and placed under a table - Mr Pinheiro walked out of the prison and immediately lodged an official protest with the Burmese authorities, a UN official said.
"Under these circumstances he felt obliged to interrupt
his mission," the UN statement said.
UN sources told the BBC that Mr Pinheiro was upset and furious at the discovery, but still hoped to return to Rangoon in May to complete his investigation.
It is no surprise that the prison authorities have been listening in to Mr Pinheiro's private interviews, says BBC correspondent Larry Jagan.
The Burmese authorities routinely bug conversations between prisoners and their families, and even their legal representatives, according to lawyers in Rangoon.
Lack of progress
Despite repeated visits to Burma, Mr Pinheiro has been unable to persuade the ruling military junta to make any meaningful gestures of reform.
Expectations were raised briefly last year, when the authorities released opposition leader Aung San Suu Kyi from house arrest.
In fact, after his last visit to Burma, Mr Pinheiro praised the prison authorities for their co-operation, and said he had been able to interview all the political prisoners he wanted to without prior notification.
But any glimmer of hope from this latest visit have now been dashed, correspondents say.
Our correspondent says that one result of Mr Pinheiro's premature departure may be to bring forward a visit by UN special envoy Razali Ismail, who has been trying to return to Rangoon for several weeks.
Mr Razali had found the regime less than anxious to accept him, our correspondent says.
He says Burma's ruling generals are now going to have to show their willingness to co-operate with the UN.