An Australian senator has accused the government of trying to whitewash its hard-line asylum seeker policies by blocking access to a detention centre holding 157 Sri Lankan migrants recently after holding them in deep for close to a month.

And a group of prominent Christian religious leaders today accused Immigration Minister Scott Morrison of committing "state-sanctioned child abuse" through the government's tough border security measures.

Under the policies, aimed at stopping asylum seekers reaching Australia's mainland by boat, customs or navy intercept the boats and asylum seekers are usually taken to camps in Papua New Guinea and the South Pacific nation of Nauru where they face long periods of detention while they are processed.

The religious leaders accused the Australian government of ‘hiding behind the false policies.’

"I have been there a number of times. I know what it looks like inside. I wanted to speak to the new asylum seekers who are being detained there," she told Reuters.

Prime Minister Tony Abbott's conservative government has boasted of its success in deterring asylum seekers and says that the policies are needed to save lives at sea and to protect Australian sovereignty.

But in a report released on Wednesday entitled "Protecting the Lonely Children", the Australian Churches Refugee Taskforce blasted the policy over its treatment of minors. There are 50 children said to be amongst the Sri Lankan detainees.

In another report it stated that a majority of the apprehended asylum seekers were not Sri Lankan but in fact Indian.

"The minister forsakes his guardianship duties when he sends unaccompanied children to the detention camp in Nauru," they said.

The Australian navy intercepted the boat en route from India and held the asylum seekers, most of whom are believed to be ethnic Tamils, on the high seas for more than three weeks before bringing them onshore on Sunday and Monday. (With inputs from a Reuters report)