The human rights group Amnesty International says there has been an upsurge in rights abuses in Burma in the last six months and is renewing calls for the military government to free more than 1,300 political prisoners. Amnesty International investigator Donna Guest said on Monday that human rights violations have increased in Burma since a May clash between pro-government supporters and members of Aung San Suu Kyi's opposition National League for Democracy, or NLD.

"There has been a serious deterioration [of human rights] since the 30th of May, not only the events of the 30th of May, but the fact that so many people have been arrested after the 30th of May," she said.

Ms. Guest says 24 people, including Aung San Suu Kyi, were arrested on that day and 52 people have been detained since then. She says some of those detained have already been sentenced to seven years in prison under an emergency law, with little or no access to a lawyer.

Amnesty International's Deputy Director for Asia-Pacific, Catherine Baber, says during the 17-day visit, her team visited three prisons and met with 35 political prisoners, including politicians, students, journalists and members of armed opposition groups.

She says the team was not allowed to visit Aung San Suu Kyi, but did meet with three members of the NLD's senior executive committee who had been released from detention and other political leaders. She says all reported that they were not allowed to engage in political activities.

Burma's military government has pledged to hold a national convention next year to draft a new constitution and prepare for elections.

But Ms. Baber says Amnesty International is skeptical of such promises.

"We have been told to be patient and that change may come soon," she said. "But these assurances ring hollow in the face of continued repression. Ultimately, there comes a time for action and that time is now."

She repeated Amnesty International's call for the Burmese government to release all political prisoners and to refrain from using the legal system to criminalize freedom of expression and peaceful association.

The Burmese government has issued a statement expressing appreciation for the visit of the human rights group - its second this year - and looks forward to future visits. The statement did not address Amnesty's allegations, but said the visit reflects the spirit of openness and cooperation in Burma as it makes a transition to democracy.