Three asylum seekers forcibly removed to Sri Lanka in 2009 are believed to have been tortured and jailed following an attempt to return to Australia, says Amnesty International.
The human rights group said today it held grave fears for the men who now risk further torture and abuse from guards and prisoners.
The development comes amid warnings from the coalition that Australia faces a surge in asylum seeker traffic following a deal between Labor and the Australian Greens.
Authorities on Friday morning intercepted asylum seeker boat carrying 59 passengers and two crew in waters north of Christmas Island - the seventh arrival since the election on August 21.
Amnesty International said two of the men - Sumith Mendis and Lasantha Wijeratne - were taken to hospital on Wednesday after claims they were beaten and tortured following an alleged new attempt to seek asylum in Australia.
It is not clear if they are still in hospital or have been returned to prison, where the third man, Indika Mendis, is being held.
Dr Graham Thom, from Amnesty International, said the return of the men to Sri Lanka when they still faced persecution meant Australia was in breach of its international obligations.
"This puts Australia at serious breach of our obligations under the convention against torture," Dr Thom told AAP.
"We are not allowed to send people back to a country where they face torture or death. And quite clearly we have sent people back who have been tortured and who are still at risk."
"We have grave fears for these three men right now."
The three men are Sinhalese fisherman, rather than Tamil as is usually the case with asylum seekers from Sri Lanka, and are understood to be at risk because of their roles in having helped to crew the boats they travelled on to Australia.
Sumith Mendis and Indika Mendis were detained in 2009 at the Christmas Island detention centre after the boat they were on was stopped by Australian authorities.
They were deported to Sri Lanka where they were arrested and handed over to the Central Investigative Department (CID).
It is understood Sumith Mendis was released but Indika Mendis was tortured while custody before being transferred to the notorious Negombo prison where he was held for eight months.
The brothers were arrested again last month on suspicion of planning to again seek asylum in Australia and are believed to have been taken to Negombo prison on August 22 along with Mr Wijeratne, who had also previously been deported from Australia.
The development came as opposition immigration spokesman Scott Morrison today seized on the arrival of another asylum seeker boat to warn three key independents against siding with Labor in negotiations on forming a minority government.
"We've had now more than 300 people arrive illegally while we've been here and others have been here in Canberra discussing who will form the next government," Mr Morrison told reporters in Canberra.
"Under a Labor/Greens alliance, supported now also by Andrew Wilkie, it is clear that Labor's policies on border protection will only get softer."
The Greens are opposed to offshore processing of asylum seekers, as is Mr Wilkie.
However, the support offered by the Greens and Mr Wilkie extends only to supply and no-confidence motions.
A spokesperson for Immigration Minister Chris Evans rejected Mr Morrison's comments, adding that Labor was committed to offshore processing.
"Once again, Mr Morrison's comments have no foundation in the truth," the spokesperson said.
"A Labor government will maintain its commitment to strong border security. The Gillard government has invested more in border security measures than any other government and has outlined a clear policy for the establishment of regional processing centre."