U.S. Homeland Secretary John Kelly says there have been countless attempts by terrorists to blow up passenger jets operated by Air Canada and U.S. airlines – plots that have been stopped because of U.S. and Canadian intelligence agencies.

"The most significant threat is a terrorist attack I think on aviation. That seems to be their Stanley Cup playoff. They want to knock down airplanes and they are trying every day to do it," Mr. Kelly told CTV's Power Play on Friday after meeting with senior Trudeau cabinet ministers on Parliament Hill.

"I can't count the number of airplanes that have not been blown up in flight, whether they are United [Airlines] or Air Canada …but I can tell you there are dozens of plots ongoing all the time." Air Canada issued a strong denial that the airline had been the focus of any terrorist plot.

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"Air Canada's policy is generally not to discuss issues of security. However there is no truth whatsoever in the suggestion that Air Canada may have been involved in such threats," spokesman Peter Fitzpatrick told The Globe and Mail.

Mr. Kelly would not provide further details, saying the information was classified, but he added that Canada and the United States are considered "hard targets" by terrorists because of the security measures the two countries have put in place and their seamless co-operation on the sharing of information, including on passengers.

Public Safety Minister Ralph Goodale did not deny that there had been terrorist threats against Air Canada when asked about Mr. Kelly's comments.

"No there is not a new specific threat against Air Canada. Obviously if that were to be the case, we would be taking a range of actions, but the secretary was not referring to a new immediate threat."

He acknowledged aircraft terrorism was of high concern but played down the immediate dangers to airline passengers.

Over the past 15 years, Mr. Kelly said, "we know there are hundreds of plots that we have discovered and ended" and that "there are dozens and dozens of ongoing plots to get to the United States or blow up airplanes."

A Homeland Security official called The Globe and Mail late Friday night from Washington to say that Mr. Kelly did not mean to imply that there had been specific threats against Air Canada or any other airline.

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"The Secretary was not referring to any specific plot or specific airlines. He was talking generally about efforts by terrorists to disrupt air travel and he used examples of airline names," said the official, who was part of Mr. Kelly's delegation to Ottawa. "He did not intend to imply specific plots about this airline."

Mr. Kelly, a former Marine general, discounted complaints from Canadians who say they have been stopped and denied entry by U.S. border agents for frivolous reasons since U.S. President Donald Trump imposed an immigration ban on refugees and visitors from certain Muslim-majority countries.

"Those who are stopped, a small handful, there is a reason for stopping them. Whatever they tell the press is their business but no one is stopped to be checked for their religion or their political opinion," he said.

Mr. Kelly said he had a wide-ranging discussions with Mr. Goodale, Foreign Affairs Minister Chrystia Freeland, Immigration Minister Ahmed Hussen and other senior ministers about the recent raft of nearly 2,000 asylum seekers crossing the U.S. border into Canada.

What perplexes officials on both sides of the border is that most of the asylum seekers had arrived in the U.S. with legitimate visas – many for only days, he said.

Mr. Kelly conceded in a separate interview with CBC that anti-Muslim sentiment in the United States could be the reason why these people are crossing the border to claim refugee status in Canada.

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"It could be. I think you could draw that conclusion. I am undecided but to come here legally from any other country and then almost push on immediately to Canada is something I don't quite understand," he said.

During a meeting of American and Canadian law enforcement agencies in Montreal last month, the United States asked Canada to provide details about the border crossers, including how they had entered the United States and what their status was there, according to a Reuters report.

Prime Minister Justin Trudeau was asked on Friday why the Canada Border Services Agency won't provide that information to U.S. authorities.

"Canada has a strong and rigorous system for processing refugees and immigrants. We do not compromise on security. We ensure that we know everything there is to know about people arriving to our shores. And at the same time, we are also committed to protecting the privacy rights of Canadians and of people in Canada," Mr. Trudeau told reporters in Houston, where he was attending an energy conference.