Investigations into leaks at the Ministry of Defence could lead to "a number" of prosecutions, the defence secretary has said.
Speaking on the Andrew Marr Show, Dr Liam Fox said he had no idea who was behind the leaking of letters and documents from his department.
But he did not discount the possibility that a cabinet colleague was involved.
He said the leaks meant the government was less likely "to put things on paper", which meant less transparency.
The latest incident occurred last month when a letter from the defence secretary to Prime Minister David Cameron was leaked to a newspaper. In the letter, Dr Fox challenged plans to enshrine the UK's aid budget in law.
Another private letter, in which Dr Fox raised concerns about proposed cuts in defence spending, was leaked last year ahead of the defence review. The defence secretary criticised the leak and ordered an inquiry.
He told Andrew Marr: "We are investigating very much at the present time and we have a number of potential court cases coming as a consequence."
Asked whether he thought a fellow cabinet minister was behind the leaks, he said: "Well, you never know, and that's the whole thing with leaks.
"They are unprofessional and they are unethical, and in being unwilling to stand up and argue the case publicly they are cowardly. It's a culture I think that's emerged in recent years and it's hugely regrettable."
Dr Fox said he had "no idea who leaks" or therefore what their motivations were but he said it meant less information might be comitted to paper.
"It also means that we are far more likely to discuss things face-to-face without necessarily other advisers being there," he added.