By Ben Packham of The Australian
Julia Gillard's Cabinet Secretary Mark Dreyfus, a Queen's Counsel, suggested the challenge was driven by domestic political concerns.
“I think when you've got the Opposition Leader in Papua New Guinea bringing a proceeding in the Supreme Court in Papua New Guinea, it does smack of politics to me,” he told Sky News.
Mr Dreyfus said Australia had an agreement with PNG to host the Manus Island processing centre as part of a long-term objective to establish a regional asylum-seeker processing framework.
Mr Namah said in a statement that he regretted taking the action against the PNG government but he had no choice.
“We will take this matter as far as necessary to ensure that the values of our nation's constitution are upheld,” Mr Namah said.
“This legal challenge also attempts to remedy the many abuses of PNG law and of ministerial powers which have given rise to the situation on Manus.”
Mr Namah said people seeking refugee status in Australia were being held “illegally and indefinitely under inhumane conditions” on Manus.
“We challenge the right of the government to make this arrangement with the government of a foreign nation, again in contravention of our constitution,” he said.
The injunction seeks to have the current detainees released and to prevent the government from receiving or detaining any more asylum-seekers from Australia.
“I am confident that our justice system will succeed in upholding this truth, where our government has so regrettably failed,” Mr Namah said.
The National Court is yet to set a date to hear the challenge, the ABC reports.
Manus Island MP Ronnie Knight also accused Mr Namah of political point scoring.
He said he should have announced his opposition to the site during the last term of government, when he was Prime Minister Peter O'Neill's deputy.
“If the shoe was on the other foot and he was prime minister, he would be pushing for Manus,” Mr Knight said.
“It's been done before and it worked, and there was a political decision to stop it. We feel if (processing) is not done here, it will be done elsewhere.”
But Liberal MP Steve Ciobo said the legal challenge was a consequence of Labor's failed border protection policies.
“It is largely understandable,” he said.
“I think they're concerned that Australia's policies are so bad, they're so haphazard ... that they're probably wondering what is this going to mean for Papua New Guinea.”