Immigration Minister Scott Morrison and key Operation Sovereign Borders officials have fronted a Senate inquiry into why documents are being kept secret.

The details of Operation Sovereign Borders need to be kept secret because it is more like a war than an immigration program, a Senate inquiry has been told.

Immigration Minister Scott Morrison fronted a Senate inquiry on Friday, accompanied by key officials involved in the operation, to face questions over why he has claimed secrecy over documents relating to the operation.

Australian Customs and Border Protection Service chief Michael Pezzullo, a key official involved in the operation, said that to reveal whether or not asylum seeker boats were being turned back or other details of the operation would be to put lives at risk and jeopardise the operation.

“Operation Sovereign Borders is not, in a sense, an immigration management program,” he said.

“It’s actually a maritime security program and it is run in accordance with the operational procedures and practices that apply to any operation – law enforcement, war-like or war operation.”

Mr Morrison said the secrecy of the operation had been key to its success, as people-smugglers used public information to develop their tactics and advise their clients.

“Since December 19 not a single boat has successfully made it to Australia and to illegally enter our waters,” he said.

Labor and the Greens used their numbers in the Senate to demand the government release documents relating to the operation, but the minister has claimed a “public interest immunity”.

The parties argue the government is not being properly accountable by not revealing whether boats have been turned back or if asylum seekers have been harmed in the process.

The minister told the committee: “It is the policy and practice of this government to intercept any vessel and, where safe to do so, remove it outside Australian territorial waters and beyond our contiguous zone.”

Asked whether this was his first public confirmation that boats had been turned back, he said that to answer the question would “put people and the operation at risk”.

The operation’s commander Angus Campbell also declined to confirm boat turnbacks, but gave a different description of what had happened during the past six weeks.

“It’s now been 43 days since illegal maritime arrivals have been transferred into immigration authorities’ control,” General Campbell told the inquiry.

Greens senator Sarah Hanson-Young seized on the answers, saying the descriptions by General Campbell and the minister were different, but they both came to the figure of zero boats.

“It doesn’t make any sense,” she said.

The minister said what was reported weekly was the number of people who arrive illegally by boat and had been transferred to immigration authorities.

“That’s what we define in that context as both arriving and of successfully making it to Australia,” he said.

Mr Pezzullo confirmed there was a difference in status between people who had been handed over to immigration detention and those who were in the temporary custody of border protection or defence personnel.

But he declined to say how many people had been taken into “custody” since December 19.

When Labor senator Joe Ludwig suggested the operation was more secretive than ASIO, Mr Morrison said there was oversight from cabinet’s national security committee and the Senate estimates process.

There were clear reasons for stopping the boats, including the prevention of deaths at sea and saving taxpayers’ money, he said, citing a cost blowout from $85 million to $3 billion a year under Labor.