The announcement also comes a day after Human Rights Watch said the number of political prisoners in Myanmar had doubled to more than 2,200 in the two years since a deadly crackdown on protests led by Buddhist monks.
The New York-based organisation issued a report calling on the government to free all prisoners of conscience.
It said the "brutality" of the military government had been highlighted by the latest detention term ordered against Aung San Suu Kyi, the opposition leader and head of the National League for Democracy (NLD).
"Burma's generals are planning elections next year that will be a sham if their opponents are in prison," Tom Malinowski, an HRW official, said at the launch of the report in New York.
| Aung San Suu Kyi has been under house arrest for 14 years of the past 20 years [Reuters]
The government has said it will hold elections in 2010, but critics say the polls are a way for the generals to solidify their nearly five-decade grip on power.
The government released 6,300 prisoners in February, saying it would allow more people to take part in the polls, but only 17 political detainees were among them.
In September 2008, more than 9,000 prisoners were released, among them 78-year-old journalist Win Tin, who was the country's longest-serving political prisoner.
Meanwhile, Myanmar's state-owned newspapers defended a decision to bar Suu Kyi from court on Friday during final arguments in her appeal against her detention.
The Nobel laureate was convicted on August 11 of breaching the terms of her house arrest after John Yettaw, an American national, swam to her house.
Prison term reduced
Aung San Suu Kyi was sentenced to three years' hard labour but Than Shwe, the head of the military, cut the term to 18 months of house arrest.
"According to the practices of the courts, any defendants are not sent to the tribunal," a commentary in the New Light of Myanmar newspaper said.
"If the defendant is a prisoner, there is no need to summon him to the court for his statements."
Yettaw was sentenced to seven years' hard labour at the same trial for swimming uninvited to her lakeside house in May, but he was freed last month after a visit by Jim Webb, a US senator.
The guilty verdict against Suu Kyi sparked international outrage and the imposition of further sanctions against Myanmar's generals, who have kept Suu Kyi under house arrest for up for 14 of the past 20 years.