Immigration and Border Protection Minister Scott Morrison has refused to say if he had read official documents before classifying them as secret under public interest immunity provisions.
Appearing on Friday before a Senate committee dominated by Labor and the Greens, Mr Morrison repeatedly clashed with senators who demanded to know why he refused a Senate request for the production of the background documents.
Senators asked him how he had assessed border protection documents before deciding they were unsuitable for release to the Senate's legal and constitutional affairs committee.
He declined to answer that question definitively.
Labor senator Kim Carr accused the minister of making a blanket ruling on the documents rather than reading each one before ruling it not be disclosed.
Senators probed an apparent discrepancy over the definition of individual asylum seekers as ''illegal maritime arrivals'' or ''IMAs'' after Mr Morrison said there had been ''zero arrivals since December 19''. An arrival, Mr Morrison said, constituted an asylum seeker being "transferred into immigration authorities".
Asked how many boats had entered Australian waters during the same period of "zero arrivals", Mr Morrison refused to respond. To do so, he maintained, would be against the public interest.
Earlier, Mr Morrison had boasted that the government's tough policies which include turn-backs and off-shore processing, was working because it had delivered the first IMA-free calendar month in 58 weeks and the first January of zero boats since 2006.
An argument ensued as Labor and Greens senators attempted to establish if the zero-IMA claim was sustainable only because the definition of an arrival excluded people aboard vessels turned around at sea, even where they had clearly entered Australian waters. In the government's weekly statement later in the day, it was revealed one asylum seeker was transferred to Christmas Island during the week due to a health condition.
In evidence to the committee, the military commander of Operation Sovereign Borders, Lieutenant-General Angus Campbell, suggested the release of the documents would represent a potential problem in relationships with Indonesia. ''The documents requested relate to operational matters I believe should not be disclosed,'' he said. ''These documents may impact upon Australia's relations with foreign states and damage those relationships.''
General Campbell used his opening statement to offer the strongest operational justification so far for the high level of operational secrecy.
He said that because Indonesian people-smugglers operated in competition with each other, they did not share what intelligence they were able to obtain about Australia's border security.
This meant information about the deployment of Australia's naval assets and manoeuvres was incomplete, making the task of getting asylum seeker boats through the net much harder.
''People smugglers would hope for any and all information that can help them understand our operations and make predictions about our border control system so they can circumvent it, and thereby sustain their business, which is currently under pressure,'' he said.
Mr Morrison, justifying his approach of releasing only the most basic material, condemned the previous government, saying its policies had been responsible for 50,000 IMAs since 2007, which by 2013 had risen to 4000 IMAs a month, and the collapse of the immigration detention system.
He said the Labor government had provided people smugglers with vital intelligence to help them beat the system.