TORONTO -- Ontario Premier Kathleen Wynne ignored opposition demands Wednesday that she apologize for low-balling the $275-million cost of the Liberal government's decision to pull the plug on a gas plant in Mississauga by $85 million.

"People are tired of the denials. They're tired of the hidden information," NDP Leader Andrea Horwath said during question period.

"They want the premier to admit -- that's all they want -- that this was wrong, and to apologize."

The Progressive Conservatives said the auditor general's report -- released on Monday -- was proof the Liberals had intentionally misled the public about the true cost of cancelling the Mississauga gas plant.

The Tories accused Wynne of also underestimating the cost of scrapping another gas plant in Oakville, which the government puts at $40 million.

"I asked the premier to apologize for the $85 million and for the future costs we're going to see in Oakville," said PC energy critic Vic Fedeli.

"Being a Liberal means never having to say you're sorry."

Wynne accepted responsibility for what she admitted was a political decision by the Liberals to cancel the Mississauga gas plant in mid-construction, just days before the October 2011 election.

However, even though she was Liberal campaign co-chair at the time, Wynne declined repeated requests to say sorry for the higher-than-expected price tag of the cancellation for the Mississauga project.

"I've been very clear that I regret that the decision wasn't made earlier," said Wynne.

"But it is a fantasy, and it's not fair to the people of Ontario, to say that we can start an infrastructure project and we can cancel it and there will not be a cost associated with that."

The premier would not provide an updated figure on the Oakville cancellation, even though the government now knows the criteria the auditor general will use to determine the true cost of scrapping that project. The auditor's report into the Oakville gas plant is not expected until August.

"I'm going to leave the accounting in the hands of the accountant," said Wynne.

"That's why I asked the auditor general to look at the Oakville situation, but the reality is I have taken responsibility for this, and I am committed that this will not happen again."

Outside the legislature, Energy Minister Bob Chiarelli also refused to offer an apology for the extra costs from the cancellation of the Mississauga gas plant, saying Wynne's actions speak louder than words.

"The premier was very clear in saying there was a problem in locating the (gas plant) sites, and that has to be responded to," said Chiarelli.

"She was extremely open in terms of broadening the investigation, broadening the committee's mandate, and I think those acts speak louder than anything else.

Auditor general Jim McCarter was scheduled to testify at the justice committee hearings into the gas plants late Wednesday afternoon.