Amnesty International has submitted a petition to the Chhattisgarh chief minister urging him to drop all charges against tribal activists Soni Sori and her nephew Lingaram Kodopi and release them "immediately and unconditionally".
Amnesty said it considers Sori and Kodopi to be prisoners of conscience who have been arrested on false charges solely because they criticised human rights violations by the security forces in Chhattisgarh.
"People from across India are calling for Soni Sori and Lingaram Kodopi's release," said Shashi Kumar Velath, programme director at Amnesty International India.
Sori and Kodopi have been in detention since October and September 2011 respectively. Sori's husband Anil Futane died Aug 2, 2013, but she was denied bail to perform his last rites.
"Soni Sori and Lingaram Kodopi's continued detention is a matter of shame for India," said Velath.
He added: "Their cases show just how far authorities in Chhattisgarh can go to silence their critics. Government of Chhattisgarh needs to stop filing politically motivated charges against Adivasis and start listening to what they have to say."
Sori, 36, a school teacher and her nephew Kodopi,26, a journalist, were critical of human rights violations committed both by the security forces and the armed Maoists in Chhattisgarh.
The Supreme Court will hear the bail applications moved by both Kodopi and Sori Sep 30. Sori has alleged that she was tortured while she was in police custody on 8 and 9 October 2011. In letters written to the Supreme Court, she said that police officials stripped and sexually assaulted her and gave her electric shocks.
A senior police official who Sori said had ordered and supervised her torture was conferred a gallantry award by the President of India in January 2012.