"To the courageous and enduring Iranians: I have been with you since the beginning of my presidency, and my administration will continue to support you", wrote Trump.
Responding to Iran's U-turn, Ukraine's President Volodymyr Zelenskiy demanded an official apology and full cooperation.
President Hassan Rouhani acknowledged his country's responsibility.
Kayhan, a hardline daily, led on supreme leader Ayatollah Ali Khamenei's "strict orders" to follow up on the "painful incident of the plane crash".
Salami had been due to explain the killing of Qassem Soleimani, the head of the Guards' foreign operations arm, in a Jan 3 USA drone strike in Baghdad, ISNA reported.
The jetliner, a Boeing 737 operated by Ukrainian International Airlines, went down on the outskirts of Tehran during takeoff a few hours after Iran launched a barrage of missiles at U.S. forces in Iraq.
On Twitter, videos showed protesters demanding that Khamenei step down because of the disaster.
AFP correspondents said hundreds of students gathered early in the evening at Amirkabir University in downtown Tehran to pay tribute to those killed in the air crash. Reuters could not verify the footage.
"Unfortunately under these circumstances, he made this bad decision, the missile was sacked and the plane was hit and then.it turned and the spot that it crashed at was here", he said, pointing to a map.
Iran's president said it was a "disastrous mistake" and apologised. "My thoughts and prayers go to all the mourning families".
The commander in chief, known for his random capitalization and spelling on the platform, collected almost a hundred retweets from a pair of tweets in Farsi commending the "brave and suffering Iranian people" who protesting Supreme Leader Ayatollah Ali Khamenei.
Canada severed diplomatic ties with Iran in September 2012, closing its embassy and recalling all diplomats.
Experts said mounting global scrutiny would have made it all but impossible to hide signs of a missile strike in any investigation, and Iran may have felt a U-turn was better than battling rising criticism overseas and growing grief and anger at home, as numerous victims were Iranians with dual nationality.
In Twitter messages, angry Iranians asked why the plane was allowed to take off with tensions in Iran so high.
The crash came hours after Tehran launched missiles at bases hosting American forces in Iraq in response to the killing of top Iranian general Qasem Soleimani in a United States drone strike.
"This is a tragedy that should not have happened", the prime minister said at a news conference in Ottawa.
The aerospace commander of Iran's Revolutionary Guards accepted full responsibility for Wednesday's accident.
Iran said it unintentionally shot down the plane, blaming it on human error and saying the passenger jet had made a sharp, unexpected turn toward a sensitive military base, according to a report by The New York Times.
Speaking on state television, Hajizadeh said he wished "I could die" when he heard about the incident.
According to Jones, Foreign Minister Zarif "got to the heart of the matter when he said that the cause of the recent disaster was a combination of human error and American adventurism".
The Conservative Party of Canada, the main opposition, said Trudeau still needs to hold Iran to account by listing Iran's Islamic Revolutionary Guard Corps as a terrorist group, and by imposing sanctions if Iran does not fully cooperate with the investigation. Ukraine said the plane was in a normal flight corridor and Iran's Civil Aviation Organisation said the airliner had not veered off its normal course.