Human rights lawyer Julian Burnside QC says the Federal Government's decision to hold 153 asylum seekers on a Customs boat on the high seas could amount to piracy.

After weeks of silence, the Government on Tuesday confirmed to the High Court the group, which includes children as young as two, was in custody on the boat.

"It looks for all the world like piracy," Mr Burnside said.

"If they went onto the Australian vessel because they had asked for help and they were offered help, then they seem to have been taken under false pretences because the Government not only publicly denied their existence it also seemed distinctly uninclined to offer them any help."

The asylum seekers say they are Sri Lankan but left from India about a month ago.

Sri Lanka has indicated it will not take them back and Mr Burnside thinks India would be unlikely to.

"Because India of course is not a signatory to the refugees convention," he said.

Immigration Minister Scott Morrison is still refusing to give any details about his plans for the group.

"The resolve of the Australian and Sri Lankan governments to stop people smuggling is stronger and greater than the people smugglers," he said from Sri Lanka.

"To anyone here who may think of getting on a people smuggling voyage to Australia: don't believe the lies that the people smugglers tell you."

Mr Morrison was in Sri Lanka for the commissioning of two Australian-gifted naval patrol boats that will be deployed for preventing people smuggling operations.

It is understood Mr Morrison also visited the war-torn region of Jaffna while he was visiting the South Asian nation.

Greens senator Sarah Hanson-Young has likened the case to the 2001 stand-off between the Howard government and the container ship the MV Tampa over where 433 asylum seekers it had rescued should go.

Mr Burnside, who was Senior Counsel for the people rescued by the Tampa, says Senator Hanson-Young may be right.

"It looks as though it's gaining that sort of significance," he said.

The Tampa's passengers were eventually sent to New Zealand and Nauru for processing.

The 153 asylum seekers at the centre of the current High Court action were intercepted in Australia's contiguous zone.

Their lawyers told the court the area is under Australian control and they are entitled to protection.

The Commonwealth's lawyers argued non-citizens in the area the boat was intercepted had no rights under the Migration Act.

However the Government has agreed to give three days' notice before making any move to transfer the asylum seekers to Sri Lanka.

The case was adjourned on Tuesday for 21 days while documents are exchanged. The court will then decide if the matter will be heard by the full bench of the High Court.

Meanwhile, a member of the Sri Lankan parliament has urged his government to eradicate the problems that led their citizens to seek asylum overseas.

Sri Lankan MP Rajiva Wijesingha told the ABC's Late Night Live program that factors pushing people out of the country must be diminished.

"I think it's up to the Sri Lankan government to try to reduce the causes of disaffection and indeed to develop situations in which Sri Lankans, both Sinhalese and Tamils, don't think that the best part of Sri Lanka is the sea leading out of it," he said.

Father fears Sri Lanka would 'wipe out' family

The father of a three-year-old girl who is on the Customs vessel has told the ABC's 7.30 program he fears his wife, daughter and extended family would be "wiped out" if returned to Sri Lanka.

"We have had no contact with them and [I] am so stressed over what's happened to them. There's no way they can return home," the man said.

"I'm separated from them. I can't go and visit them and it's because of that my wife decided to take this perilous journey.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 7 minutes 25 seconds 7 m Febrina's father talks to 7.30

"I hope the Australian Government will safeguard my family because if they are returned to Sri Lanka my whole family would be wiped out."

In Sri Lanka, Mr Morrison has also been defending the forced return of a separate group of 41 Sri Lankans intercepted close to the Cocos Islands.

Some of the group claim they were abused, given little food and treated "worse than dogs" by Australian authorities mid-sea after their boat was turned back.

Mr Morrison says the claims are without merit.

"I find those allegations offensive and reject them absolutely," he told reporters.

The group, which includes four women and nine children, have appeared in court charged with illegally leaving the country.

Twenty-seven people in that group have been bailed by a court in Galle, while five people have been remanded in custody. Their next court hearing is July 14.