Border secrecy must remain: PM

Details about the federal government's turn-back-the-boats operation still remain a secret despite it reaching a successful six-month milestone.

"I'm not declaring victory; there's no hint of mission accomplished," Prime Minister Tony Abbott told reporters in Canberra on Thursday.

He was referring to Operation Sovereign Borders being able to prevent the successful arrival of any asylum-seeker boat since December.

But Mr Abbott refused to disclose how many boats had been turned back because he doesn't want to compromise the effectiveness of operations.

"A full account of all of this will one day be given, but not yet," he said.

What we do know is that boats have stopped leaving Indonesia, and the government "understands" no asylum seeker has died during the operation.