At least 15 political prisoners were freed from Myanmar jails on Monday, activists said, following an announcement in state media that a total of 514 detainees would be released.
A spokesman for the democracy movement Generation 88 told AFP that those freed included eight dissidents from Yangon's notorious Insein prison, while the rest were from other parts of the country.
Nay Win, a member of opposition leader Aung San Suu Kyi's National League for Democracy (NLD) party, was one of the political prisoners to walk free from the Yangon prison late Monday.
He said he was sentenced to seven years imprisonment in 2008 for defamation because of comments he made accusing judges of corruption.
"Our lives are destroyed, although we are still alive," the 50-year-old told AFP at the NLD party headquarters in Yangon.
"I thank (Mother Suu) for our release. I do not want to thank them," he said, referring to the reformist government of former general Thein Sein.
Two foreign inmates -- one Indian and one Chinese national -- were also freed from Insein on Monday, Nay Win said.
Television news earlier reported that President Thein Sein "gives amnesty for a total of 514 prisoners" in a rare breaking news update.
It said the pardons were aimed at the "stability of the state and eternal peace, by respecting humanitarian grounds... and also to have friendship and goodwill in relations with neighbouring countries".
The report, which said the release included "foreign prisoners from the prisons around the country", comes a day before the Myanmar leader is set to embark on a visit China, followed by a trip to the United States, which has long called for the release of all jailed dissidents.
Myanmar has granted amnesty to hundreds of political prisoners as part of reforms that have caused a dramatic thaw in relations between the West and the long-isolated nation formerly called Burma.
Estimates of the exact number of political detainees still locked up vary but Generation 88, which played a key part in a 1988 uprising against the former junta, has said around 300 activists still languish in jails around the country.
Phil Robertson of Human Rights Watch welcomed the amnesty, but said it was not yet clear "what it means and how significant it is".
"The problem is there is a lack of transparency from the Burma government about who is a political prisoner, where they are, and how many are left," he said.
Thein Sein will visit China until September 22 and is then set to embark on a trip to the United States to attend a United Nations General Assembly on September 24.
His visit coincides with a high profile trip to the US by Suu Kyi, herself freed from years of house arrest in 2010, who left Myanmar for a near three week trip on Sunday.
The democracy champion, who is now an elected politician, used her long-awaited acceptance speech for the Nobel Peace Prize in Norway in June to call for the release of Myanmar's remaining political prisoners, warning of the risk that "the unknown ones will be forgotten".