THE Greens have hit out at unconfirmed reports Australian authorities attempted to give more than 150 Tamil people back to the Sri Lankan government.

Reports emerged last week about a boat carrying some 153 Tamils attempting to get to Australia from India, but they remain unconfirmed by the Australian Government.

But concern about the fate of those reported on board are heightening, after reports the Tamils, a long-persecuted peoples in Sri Lanka, were due to be handed back to that nation's government.

The uncertainty surrounding the issue, and lack of information, was criticised by Greens leader Senator Christine Milne on Wednesday.

She said if the reports were correct, handing back potential asylum seekers to those persecuting them could amount to a breach of Australia's international obligations under the refugee convention.

"Australians deserve to know just how low our government is prepared to go for their domestic political mantra," she said.

The Abbott government's policy since starting its Operation Sovereign Borders has been not to comment on such matters unless "significant", such as loss of life or emergency situations.