Story highlights High Court has ruled that offshore detention does not breach Australian law

Over 260 asylum seekers now face deportation from Australia to Nauru

(CNN) Australia's High Court has rejected a challenge to the government's right to hold asylum seekers on Manus Island and Nauru.

The court challenge -- brought by the Human Rights Law Center (HRLC) -- centred around the legality of the Australian government to detain people on foreign soil.

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On Wednesday, the court ruled that the Australian government's role in funding and participating in offshore detention does not breach Australian law. It means that over 260 people who had been sent to Australia for medical care are likely to be sent back.

"We're disappointed with the ruling," said the HRLC's director of legal advocacy, Daniel Webb. "We now look to the Prime Minister to step in and let them stay."

More than 1,400 people are being held in immigration detention on the islands while they wait for their asylum claims to be processed. Some have been there for more than three years. The average length of detention, according to the latest government figures, is 445 days.

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