UK minister Andrew Mitchell begins visit to Burma
The UK's International Development Secretary has called for the release of all Burma's political prisoners on the first day of a visit to the country.
Andrew Mitchell is due to meet top government officials and the leader of Burma's democratic opposition, Aung San Suu Kyi, during his three-day trip.
He told the BBC there were "grounds for cautious optimism" about the prospect of reform.
But he said there must be action as well as words from the regime.
Burma held its first elections in two decades almost a year ago - polls which saw military rule replaced with a military-backed civilian-led government.
Since then the government has freed Aung San Suu Kyi and held a dialogue with her. It has also released several hundred political prisoners.
But opposition groups estimate there are still between 600 and 1,000 detainees currently being held in prisons around the country, including journalists, pro-democracy activists and monks.
Their detention is a crucial reason why Western nations maintain sanctions against Burma.
Speaking to BBC Radio 4's Today programme, Mr Mitchell said "enough had changed to justify a visit and engagement like this".
"It is clear that there are grounds for cautious optimism, but the picture is mixed," he said.
"On the one hand, there is now proper dialogue between Aung San Suu Kyi and the government and they have released some of the political prisoners.
"But, on the other hand the ethnic conflicts which besmirched Burma continue and we've also seen also a failure to release a large number of political prisoners, some of whom are key to Burma's future."
He said he had been given "unfettered access to all levels of government" during the visit, adding: "So in terms of a dialogue there is clearly significant movement, but there are a lot of words still, we need to see actions, and in particular, we need to see these political prisoners released."
The minister cited the example of one particular political leader who was able to operate freely four-and-a-half years ago - when Mr Mitchell last visited the country in opposition - but was now locked up.
"One of the litmus tests we set for the regime is when are they going to release him," he said.
"It's quite wrong that he's been incarcerated and when they release him that will send a very positive signal about engaging with the people who do not support the regime but want to be part of Burma's future."
Mark Farmaner, from the Burma Campaign UK, viewed the possibility of reform with some scepticism.
"The big question is why they have made these reforms, and the suspicion is, this is not some genuine move towards democracy," he told the BBC.
"But rather, they are trying to take off maybe the rough edges of the dictatorship in an attempt to try and get sanctions lifted and try and get more international legitimacy."