Aung San Suu Kyi and her party are frustrated at the lack of progress
A UN human rights envoy has said the situation in Burma remains challenging, and that there had been no improvement since his last visit seven months ago.
Tomas Ojea Quintana met political prisoners in Rangoon's Insein jail and government officials during his visit.
But he was not given access to either General Than Shwe or the detained opposition leader Aung San Suu Kyi.
US Secretary of State Hillary Clinton said the US was looking for new ways to move the situation forward in Burma.
"The human rights situation in Myanmar [Burma] is still challenging. It's difficult to affirm that the human rights situation has improved," Mr Ojea Quintana told reporters in Rangoon.
Mrs Clinton - who is on a regional tour of Asia - said earlier this week that the US "is looking at what steps we might take that might influence the current Burmese government and we're also looking for ways that we could more effectively help the Burmese people."
The US, the EU and other countries apply political and economic sanctions against Burma because of its poor human rights and democracy record.
The National League for Democracy, Burma's opposition party led by Ms Suu Kyi, this week re-asserted its belief that sanctions remain a useful tool.
"We would be pleased to propose they be revoked when one of our three pre-requisites has been met," Soe Aung, spokesperson for the Forum for Democracy in Burma, told the BBC News website.
These are the release of all political prisoners, the re-convening of parliament and a review of the constitution passed by the regime last year, or the start of a dialogue without preconditions, he said.
Meanwhile, Indonesian Foreign Minister Hasan Wirajuda, on a visit to Australia, criticised the rights situation and the lack of democracy in Burma.
His comments, reported on Radio Australia, come a week ahead of a summit of the Association of South East Asian Nations (Asean), of which Burma is a member.
Dr Wirajuda told the radio station that the international community must stay engaged with Burma, arguing that pressure and sanctions had not worked.
Burma's ruling generals say they have a "roadmap to democracy" which includes elections under a new constitution, a process the opposition says is fundamentally flawed.