Justice Minister Peter MacKay said there is an "ongoing investigation" involving Ontario cabinet minister Michael Chan, suspected by Canada's spy agency of being too close to the Chinese government at a time when Beijing has been accused of trying to exert foreign influence.

"Clearly there are people outside our country, as inside our country, who would seek to exert influence," Mr. MacKay, who would not comment on specifics of the probe, said in Ottawa on Tuesday.

In an interview with The Canadian Press, he added: "I think it's fair to say it's incumbent upon all public officials to be very diligent in how they conduct themselves and to be wary of that fact, wary of who they're talking to, wary of what, if anything, that they would disclose in those discussions."

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Mr. MacKay's comments reinforced the gulf between the federal and Ontario governments over the handling of Mr. Chan. Premier Kathleen Wynne on Tuesday defended her minister, saying any concerns about Mr. Chan were "baseless," and the federal spy agency's suspicions lacked substance

"All of those have been addressed. There was nothing of substance that has been brought forward to me," the Premier said during an unrelated factory tour in Cambridge, Ont. "Michael Chan has done his job with respect and with honour. He has worked incredibly hard for the people of Ontario and he continues to do so." She added: "He has my trust."

CSIS was concerned that Mr. Chan was susceptible to foreign influence and took the extraordinary step of briefing Queen's Park on the matter in 2010, The Globe and Mail revealed on Tuesday. Mr. Chan was never accused of espionage, nor was he under formal investigation. The minister dismissed CSIS's concerns in an October interview with The Globe.

The CSIS affair took place during the tenure of Ms. Wynne's predecessor, Dalton McGuinty. Mr. McGuinty's then-chief of staff was briefed on the matter, The Globe reported. The matter was brought to the province's Integrity Commissioner, but the province has not said which of CSIS's concerns were vetted and how. It is not clear that such a case would even fall under integrity guidelines, and The Globe was unable to obtain the commissioner's notes on the matter.

On Tuesday, Ms. Wynne suggested that no one told her about the CSIS concerns when she succeeded Mr. McGuinty in 2013. She said she learned about the matter when The Globe began making inquiries last year.

"It was raised because there were reporters, from your organization, who were asking questions once again and I went back to my staff and said, 'You know, what is the situation?' And this is the situation: that in 2010, these concerns were raised, nothing of substance was ever brought forward," she said. "As I say, this is a man who has worked incredibly hard, there has been no substantive concern raised and these matters were dealt with in 2010."

The opposition Progressive Conservatives said Ms. Wynne's reassurances do not go far enough. They called on her to launch a full investigation into Mr. Chan.

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"When CSIS are monitoring active members of this government, the Premier needs [ to ] take this seriously and thoroughly investigate this matter. Ontarians deserve the truth," PC House Leader Steve Clark said in a statement.

He pointed out that the CSIS probe is only one of several into the provincial Liberals. The OPP is also investigating the alleged bribery of a former Liberal candidate, the cancellations of gas-fired power plants and ORNGE air ambulance.

Ms. Wynne promoted Mr. Chan last year to become International Trade Minister, responsible for building Ontario's economic ties with several countries, including China. Asked if Mr. Chan has had to make any changes in response to CSIS's concerns, Ms. Wynne said: "There were no matters of substance that were brought forward."

Asked if CSIS overreached, Ms. Wynne stopped short. "I'm not going to speculate on what CSIS does or doesn't do," she said. "What I'm saying is there was nothing of substance brought forward to me. This is a man who works incredibly hard."