The father of a fallen U.S. army captain who made headlines for taking on Donald Trump during the American presidential race has cancelled a talk he was set to deliver in Toronto.

Although organizers have said Khizr Khan's travel privileges are under review, the circumstances remain unclear as Canadian officials told CBC News they know of no reason why the Pakistani-born man would be denied entry to the country. U.S. officials also confirmed that they would not have gotten in touch with someone in advance of a planned trip.

Khan, who famously offered up his copy of the U.S. Constitution to the then-presidential hopeful who vowed to implement a ban on Muslims entering the U.S., was scheduled to speak at a luncheon hosted by Ramsay Inc. on Tuesday.

But on Monday, organizers of the luncheon issued a statement saying that Khan would not be travelling to Toronto.

"Late Sunday evening Khizr Khan, an American citizen for over 30 years, was notified that his travel privileges are being reviewed," Julia McDowell of Ramsay Inc. said.

Circumstances of review unclear

The statement goes on to quote Khan, saying he offered his sincere apologies for the cancellation.

"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. I have not been given any reason as to why," the statement quotes Khan as saying.

CBC News reached out to Khan's law office directly, which said in an email it had no comment.

The circumstances of the reported travel review aren't clear. Neither Khan nor Ramsay Inc. would provide specifics about what the review entailed or say more about the "turn of events."

Asked who issued the notice of review to Khan, Bob Ramsay told CBC News, "I don't know exactly who it was, but I do know for sure that it was American."

In a statement to CBC News, U.S. Customs and Border Protection said it does not contact travellers in advance of their travel out of the United States.

"With respect to Global Entry or trusted traveller membership, CBP's engagement is about the status of membership in the program, not any particular travel itself," the statement said, adding that any U.S. citizen with a passport can travel without trusted traveller status.

The agency would not comment on Khan's claim, citing privacy considerations.

Immigration, Refugees and Citizenship Canada told CBC News on Tuesday that the federal department did not know of any restrictions that would have prevented Khan from entering the country. 

"American citizens are not required to apply for either an Electronic Travel Authorization (eTA) or a temporary resident visa (visitor visa) to enter Canada," spokesperson Nancy Caron wrote in an email. 

'So that we don't all end up sacrificing'

According to its events page, Khan's Ramsay Talk was to focus on what could be done about "the appalling turn of events in Washington — so that we don't all end up sacrificing everything."

Khan's son Capt. Humayun Khan, 27, was killed in Iraq in 2004 when a car loaded with explosives blew up at his compound.

A Muslim challenges Trump at the DNC1:57

"Have you ever been to Arlington cemetery?" Khan asked Trump, speaking at the Democratic National Convention in Philadelphia last July.

"Go look at the graves of brave Americans who died defending United States of America. You will see all faiths, genders and ethnicities. You have sacrificed nothing."

On Monday, U.S. President Donald Trump issued a new travel ban, nearly a month after a federal court refused to reinstate an earlier executive order that blocked travellers from seven Muslim-majority countries, and halted entry to refugees.

Under the new ban, visa processing for travellers from Iran, Somalia, Sudan, Yemen, Syria and Libya will be suspended for 90 days. It is expected to go into effect March 16.

With files from Laura Fraser