Canada's auditor general on Tuesday accused the defense department of misleading lawmakers on the US-led F35 fighter jet program's soaring costs, in a scathing report.

Military officials were so committed to buying the F35 that they "did not exercise due diligence" for the most expensive military procurement in Canadian history, and made key decisions without approvals or proper documentation, said Auditor General Michael Ferguson.

"The department did not provide parliamentarians with complete cost information or fully inform decision makers about risks created by problems encountered in the (F35) program," he said.

"Only the most optimistic (cost) scenario was put forward," and "key approvals (were) obtained after decisions were made."

Ottawa announced in July 2010 its intention to buy 65 next-generation F35 Lightning II fighter jets to replace its aging fleet of CF-18 Hornet fighter jets, for $9 billion plus $7 billion for aircraft maintenance.

Ferguson estimated the true cost at more than $25 billion for the F35, a US-led global aircraft which is also known as the Joint Strike Fighter.

He also said, "the department did not acknowledge that the decision to purchase the F35 was well underway four years before it was officially announced" in 2010.

And the military breached rules by keeping the government's procurement authority out of the loop. Public Works only became involved "late in the process" and "endorsed the decision to sole source the acquisition of the F35 without required documentation and completed analyses," he said.

The opposition pounced on the report to accuse the Prime Minister Stephen Harper's Conservative government of mismanaging the F35 procurement.

"The government knew the F35s were going to cost more than anticipated, but they intentionally hid it from parliament and the public," said New Democrat MP Christine Moore.

"This was an outrageous attempt to try and pull the wool over the eyes of Canadians."

The government reacted by saying it would boost oversight, freeze its allocation for the fighter jet purchase at the original $9 billion, and transfer responsibility for the procurement to the Public Works ministry.

"Canada will not purchase new aircraft until further due diligence, oversight, and transparency is applied to the process of replacing the Canadian Forces' aging CF18 fleet," Public Works Minister Rona Ambrose said in a statement.

Canada has been a partner in the Joint Strike Fighter program since 1997, with Australia, Denmark, Italy, Netherlands, Norway, Turkey, and Britain, as well as one of its most ardent supporters.

The defense department says it expects the first aircraft to arrive in Canada in 2019.