The United Nations human right envoy to Burma, Paulo Sergio Pinheiro, has said there has been a serious deterioration in political conditions in the country.
Aung San Suu Kyi has refused freedom until conditions improve
He was speaking to the BBC in Bangkok after a six-day visit to Burma.
Mr Pinheiro specifically highlighted the large numbers of political prisoners held by the military junta.
He earlier said that opposition leader Aung San Suu Kyi had refused an offer to be freed from house arrest, unless her supporters were also released.
"All the political prisoners must be released," Mr Pinheiro told a press conference in Bangkok. "Prison is hell. It is unacceptable."
"I am so frustrated. And I am more embarrassed because I have to meet those prisoners for the fifth or sixth time," he said, referring to his repeated visits to the nation's jails.
Mr Pinheiro said that this year the releases had dropped to a trickle.
Among those still detained were senior leaders of Aung San Suu Kyi's National League for Democracy (NLD), who were on average 80 years
"These old gentlemen, their place is not in prison," he said.
He told the BBC on Monday there was no evidence of any basic freedoms in Burma at the start of what the government has described as a seven-step plan to national reconciliation.
He described his view of the situation inside Burma as shifting from cautious optimism to scepticism, although some opportunities remained.
Talks with Suu Kyi
Mr Pinheiro told reporters on Saturday that Aung San Suu Kyi would not accept liberty until 35 colleagues in the NLD were also released.
The UN envoy, who spent two hours with the democracy leader, said she wanted a fair and independent inquiry into clashes between her supporters and pro-government demonstrators, after which she was taken into detention.
He said he had forwarded the request to the junta, and offered to conduct the inquiry, but had received no response.
Mr Pinheiro said such an investigation could become "some sort of re-foundation for the dialogue for national reconciliation, for the political process."
The Burmese Government told Mr Pinheiro that Aung San Suu Kyi was no longer held under any security law.
But Mr Pinheiro said Suu Kyi's telephone was cut and there were
"security arrangements" around her house.
The UN envoy defended his record in the country, following sharp criticism of his non-confrontational approach by US Congress last week.
"Pressure is not a good thing only. You have to express, appeal,
engage, dialogue," he said.