The campaign group Human Rights Watch has accused the state government in Gujarat in India of failing to bring to justice those responsible for the deaths of more than 1,000 Muslims last year.
The group has published a report saying the federal authorities should now take over the investigation of those suspected of organising the killings.
It accuses the state government of sabotaging the inquiry.
Human Rights Watch said that more than 100 Muslims had been charged over alleged involvement in the killing of Hindu activists aboard a train - the incident which sparked the violence.
However no Hindus were charged over the ensuing attacks which left many Muslims dead.
From the newsroom of the BBC World Service