Cabinet Minister Mitch Fifield has described the leaking of classified defence documents as "unhelpful", as former prime minister Tony Abbott denied he was behind the papers going public.

Key points: Tony Abbott says he had nothing to do with defence documents leak

Tony Abbott says he had nothing to do with defence documents leak Senator Mitch Fifield says document leak serious, warrants inquiry

Senator Mitch Fifield says document leak serious, warrants inquiry Some Coalition ministers say situation has created tension in the party

A report in The Australian newspaper referenced "several sections of the draft white paper" produced under Mr Abbott and former defence minister Kevin Andrews.

At the heart of the revelation was the timing of when the Government planned to have the next fleet of submarines in action.

The leaked documents allegedly reveal Malcolm Turnbull plans to deliver the next fleet of submarines in the 2030s, almost a decade after Tony Abbott planned to.

The report quoted Mr Abbott as saying he was "flabbergasted" by the decision.

Senator Fifield told Sky News the leaking of any classified documents was "always serious".

"It's important that governments, regardless of persuasion, can have confidential deliberations, particularly on issues of defence and national security," he said.

"It is entirely appropriate the secretary of the Department of Defence has initiated an inquiry.

"Obviously anyone who releases classified information isn't trying to be helpful.

"We are a good and cohesive team; we don't know where this particular leak came from, that's why it's important to have an inquiry."

Mr Abbott issued a strongly worded statement and denied any involvement.

"I don't leak; I don't background against colleagues. If I've got something to say, I say it," he said.

Senator Fifield defended Mr Abbott's right to comment on the leaked documents.

"Former leaders of the party and former prime ministers have a right to make comment," he said.

The situation has created tension within the Coalition, with sources telling the ABC it appeared Mr Abbott had broken his promise not to undermine his successor.

"Abbott's still in the angry phase — people are starting to get annoyed," one minister said.

"It's scrappy, it's just not useful," said another minister, but tried to differentiate the situation to what was experienced during the Rudd-Gillard years.

"The noise is coming from quite a small group; Rudd had a bloc of support."

A Coalition backbencher described it as "the last death roll of a past leader".

"If Tony Abbott had any thoughts of a return to the prime ministership they died with today's Australian newspaper," the backbencher said.

It is the latest piece of commentary from the former prime minister, after he urged the Government to chase further spending cuts and avoid changes to negative gearing.

Mr Abbott has also outlined his opposition to the Safe Schools program.