Hong Kong (CNN) -- At least 58 political detainees were among hundreds of prisoners released in Myanmar as part of an amnesty announced on Monday, a prisoner rights group said.
According to state-run newspaper, New Light of Myanmar, 514 prisoners, including foreigners from prisons around the country, were freed on humanitarian grounds and to "ensure the stability of the state and eternal peace."
The move comes ahead of Burmese President Thein Sein's visit to the United States next week to attend the United Nations General Assembly, raising questions about the timing of the release, according to one prisoner rights group.
"We think the prisoners are a bargaining chip," Bo Kyi, joint secretary of the Assistance Association for Political Prisoners (AAPP), told CNN. He said the move was just a show for the international community so that Myanmar's president could enter the United States -- Washington recently eased its travel ban on Burmese leaders to accommodate the visit.
"If the Burmese authorities were really honest, they would release all the political prisoners unconditionally," Bo Kyi added.
"If they wanted, they could release them tomorrow. But the problem is they're not recognized as political."
He said the AAPP estimated that around 300 political prisoners remained in detention in Myanmar, with many experiencing poor conditions and brutality.
The Myanmar government does not make a distinction between ordinary and political prisoners.
AAPP is a nonprofit organization that gathers information on political prisoners and their conditions in Myanmar, as well as providing assistance to the prisoners and their families.
The Sein government has released hundreds of political prisoners in the past year, as part of a series of political reforms after decades of repressive military rule. Western governments have responded to the efforts by easing sanctions on the country.
The authorities have also engaged in peace talks with rebel ethnic groups and allowed the opposition party of democracy campaigner Aung San Suu Kyi to participate in by-elections for the national parliament in April.
Suu Kyi's party, the National League for Democracy, won nearly every seat up for grabs in those elections, and she and other newly elected NLD members have taken up their seats in parliament.
Suu Kyi, who spent years under house arrest in Myanmar, is currently in the United States where she will receive the Congressional Gold Medal, the top honor awarded by the U.S. Congress. But she is also under political pressure at home to lobby the U.S. to remove remaining embargoes on the once-reclusive state.
Despite considerable progress in Myanmar, concerns remain over whether the military establishment, which maintains overwhelming control of parliament, is committed to deep and lasting political change.
The current administration also been accused by rights advocates of cracking down particularly harshly on the Rohingya, a stateless ethnic Muslim minority, amid violence between Buddhists and Muslims in the country's Rakhine state.
The persecution of the Rohingya was something the previous ruling junta was accused of during decades of authoritarian rule. At the height of the violence, thousands were forced to flee into neighboring Bangladesh and Thailand, with many forced back at the border.
The recent unrest, which has left thousands of people homeless, has tested the efforts of Sein's administration to seek reconciliation with Myanmar's different ethnic groups and move the country toward more democratic governance.