One thing, at least, appears certain – Khizr Khan, the father of an American soldier killed in Iraq and who clashed last year with Donald Trump, will not be delivering a speech in Toronto on Tuesday lunchtime.

Mr Khan was due to speak at an event hosted by the Toronto-based Ramsay Talks. But the event’s organiser, Bob Ramsay, posted a message on Facebook, saying that Mr Khan, an American citizen for more than 30 years, was notified that his "travel privileges were being reviewed".

“As a consequence, Mr Khan will not be travelling to Toronto on March 7th to speak about tolerance, understanding, unity and the rule of law. Very regretfully, Ramsay Talks must cancel its luncheon with Mr Khan. Guests will be given full refunds,” it said,

Mr Ramsay said that Mr Khan offered his sincere apologies to all those who made plans to attend on 7 March.

“This turn of events is not just of deep concern to me but to all my fellow Americans who cherish our freedom to travel abroad,” he quoted Mr Khan as saying. “I have not been given any reason as to why. I am grateful for your support and look forward to visiting Toronto in the near future.”

That, at least, is what organisers claim happened to the Pakistani-born US citizen who was slated to speak in Toronto on “tolerance, understanding, unity and the rule of law”.

The New York Daily News quoted a State Department official as saying there was no US State Department procedure for reviewing “travel privileges” and that anyone with a valid US passport can enter and leave the US.

Khizr Khan spoke at a Clinton rally in New Hampshire a few days before the election (Getty)

Rather, the official said that it was up to other countries, such as Canada, to admit US citizens or not. The Canadian Foreign Ministry has yet to comment.

When The Independent connected Mr Khan by email, he replied: “Thank you. I have no comments.” Mr Ramsay also failed to respond to inquiries.

Mr Khan has been a vocal critic of the President, and some of those criticisms were quoted in the event listing.

“Donald Trump consistently smears the character of Muslims, he disrespects minorities, women, judges, even his own party leadership,” Mr Khan last week told the Toronto Star. “He wants to build walls and ban us from this country.”

Mr Khan first made national headlines when he appeared at the Democratic National Convention and blasted Mr Trump, memorably asking if the Republican candidate had read the Constitution while holding up a pocket-sized version of the document.