Burma's main opposition group says the government has freed about 200 jailed dissidents in its latest gesture of political reform, but rights groups say it it not enough.

The 200 are among the more than 6,000 inmates from around the country who are being freed on what the Burmese government calls humanitarian grounds.

The most prominent freed dissident is popular Burmese comedian Zarganar . He angered the government by accusing it of a sluggish response to a 2008 cyclone that left about 140,000 people dead or missing. He was sentenced in 2008 to 59 years in prison.

Burmese authorities also freed an ethnic minority rebel leader of the Shan State Army North, Say Htan. He was sentenced to more than 100 years in 2005.

But international human rights groups say they are disappointed that most of Burma's more than 2,000 political prisoners are still behind bars.

United Nations human rights investigator Tomas Ojea Quintana tells Reuters news agency that Burmese leaders told him they have been reluctant to free political prisoners because it could spark demonstrations similar to the ones that toppled several Middle Eastern countries.

Quintana pointed out that opposition leader Aung San Suu Kyi has been travelling around Burma since she was freed last year and that there has been no such instability.

In the United States, Democratic Representative Joseph Crowley, a long-time advocate for human rights in Burma, says he is glad that some political prisoners are free. But he said he is also disappointed that not all were released. He is urging the Burmese government to take bold and significant action towards true democratic reform.

The head of the Senate Foreign Relations Committee, Democrat John Kerry, told the French News Agency that a number of things have happened in Burma which open up cautious hope that a transition is taking place.

The Burmese military handed power in March to an elected civilian government. But critics say the new government is dominated by retired army officials. In recent months, Burmese President Thein Sein has made several overtures toward the opposition, loosened some controls on the media and started a dialogue with Aung San Suu Kyi.

Burma still faces economic and political sanctions from the United States and European Union, which insist on the release of all Burmese political prisoners.