By politics.co.uk staff
Liam Fox has said the leaks which have hit his department in recent months are "unethical and unprofessional".
The defence secretary's comments come after reports earlier this month that he believes a Cabinet colleague may have been responsible for the most recent leak.
A letter from Dr Fox to David Cameron, seen by members of the Cabinet on the national security council, in which he questioned Britain's overseas aid spending raised eyebrows in Whitehall.
It followed a similar leaked letter last year in which Dr Fox warned against drastic cuts to the armed forces in the comprehensive spending review.
"You never know and that's the whole thing with leaks," he told BBC1's The Andrew Marr programme.
"They're unethical and unprofessional. They're also cowardly. It's a culture which has emerged in recent years which is hugely regrettable."
He warned that greater leaks would deter ministers from putting their concerns in writing and resort to face-to-face conversations instead.
"It's hugely regrettable. We are however investigating very much at the present time and we have a number of potential court cases coming as a consequence," he added.
The defence secretary used his interview to suggest that increased fighting in Afghanistan was a sign that the situation was improving.
"It is still very violent," he said, talking about Lashkar Gah.
"We have been taking space from the Taliban. Of course they're going to resist, when we do that.
"This measure that has increased violence does not indicate in any way that we are losing in this conflict. In many ways it suggests we are taking more and more territory, they're resisting and there's fighting in that space. That's exactly what the military would tell you is to be expected."