Bangkok: A University of Sydney academic has urged delegates at a human rights conference to go soft on the Sri Lankan government, which has refused to investigate war-time atrocities that allegedly occurred at the end of its civil war five years ago.

Danielle Celermajer, an associate professor at the university, told 100 delegates they should be "mindful of the heightened sensitivity and fragility" at the conference in Bangkok after Sri Lankan authorities threatened to withdraw its military and police participants.

A Tamil woman holds a photo of her husband who disappeared during the final stage of the Sri Lankan civil war. Credit:Getty

"While we will all no doubt find ourselves on occasion wishing to question the legitimacy of claims being made by Sri Lankan authorities, I would ask us to keep in mind the minimal positive impact that such confrontations would in fact have and their potentially deleterious effect on the conference," Dr Celermajer said in a confidential letter to delegates obtained by Fairfax Media.

"The stark reality is that if the Sri Lankan authorities feel themselves under attack, they will leave. They have made this clear to us," she said.