OTTAWA—The federal spending watchdog added fuel to the fire Thursday by suggesting Conservative cabinet ministers kept Canadians in the dark about the escalating cost of the planned purchase of F-35 fighter jets.

Senior members of Prime Minister Stephen Harper’s government would have known that the cost of the aircraft had shot up to $25 billion by the time of the 2011 election but publicly stuck to a lower estimate of $15 billion, Auditor General Michael Ferguson said.

“I can’t speak to individuals who knew it, but it was information that was prepared within National Defence, and it’s certainly my understanding that that would have been information that, yes, that the government would have had,” he told reporters after appearing at a Commons committee. He added that he was referring to members of cabinet.

Opposition MPs continued to hammer the government over the ongoing F-35 procurement effort, which Ferguson found was plagued by cost overruns and a lack of accurate of information for members of Parliament.

“I have a very direct question,” Liberal Leader Bob Rae said as he faced Harper in the Commons’ question period. “When was the Prime Minister first aware that the true cost of the proposed aircraft was $25 billion? On what date was he aware of this fact?”