The ousted executives of Ontario's embattled air ambulance service let the province down, Premier Dalton McGuinty said Tuesday amid angry calls for his health minister's resignation in the wake of a criminal probe of the agency.

The former leadership of Ornge, an agency that receives $150 million a year from the province, reassured the government that everything was fine after it came under fire for high salaries and questionable business practices, said McGuinty.

Those reassurances proved to be "inaccurate" and "false," he said.

"The leadership there clearly let the front-line workers down," McGuinty said. "I would take it a step further, in fact, to say that they let Ontarians and our government down."

The government has since cleaned house at the agency, replacing former CEO Chris Mazza -- who was paid $1.4 million a year -- and its board of directors.

But McGuinty insists Health Minister Deb Matthews should keep her job, despite opposition calls for her resignation.

NDP Leader Andrea Horwath said Matthews ignored complaints about Ornge raised by the opposition parties and whistleblowers at the agency for more than a year. She didn't act until allegations of wrongdoing became front-page news, she added.

"It seems to me that the minister has no choice at this point," Horwath said.

"She's either not competent at the job or, for some reason, was prepared to ignore all of the warning signs for more than a year."

Matthews "looked the other way" even when paramedics and members of the air transport industry tried to warn her that something was going on at Ornge, said Opposition Leader Tim Hudak.

"I'm worried that their instinct more is to cover up what happened, than actually get to the bottom of it," he said.

The opposition parties also pointed out that former health minister David Caplan was forced to resign in 2009 after a damning auditor's report about eHealth, which found that nearly $1 billion was spent to develop electronic health records with very little to show for it.

But Matthews insisted Tuesday that she's "not going anywhere," saying Ornge executives lied to her when the government started asking questions.

The minister's refusal to step aside is "limiting the scope" of an investigation that could reach all the way to her office, the Opposition charged.

Matthews called those allegations "outrageous and untrue."

"I can assure you that the Ontario Provincial Police do not take orders from me or any of my colleagues," she told the legislature.

"They will do exactly the investigation that they want to do, completely unencumbered by any political direction."

Last week, Matthews called in the cops to investigate "financial irregularities" at Ornge after receiving a report from a team of about 30 forensic auditors who were poring over the agency's books.

She's also ordered Ornge's new management to shut down the maze of for-profit subsidiaries that were created with the government's approval.

Investigators are now sorting out whether any public money was used for personal gain. Auditor general Jim McCarter is also expected to table his value-for-money report on Ornge in March.

The NDP and Tories want an all-party legislative committee to look into Ornge, warning that if the full story doesn't come to light, it might happen again.

Horwath pointed to reports that Ornge's new government-appointed CEO is warning potential whistleblowers to keep quiet or risk going to jail for obstructing a criminal investigation. A committee would allow the public to find out exactly what went on at Ornge.

"We've already had scandals at eHealth, we've had scandals at the lottery and gaming corporation, now Ornge," Hudak said.

"We've got to cauterize this wound. We've got to put an end to it."