Many on board were Iranians with dual citizenship, while 57 held Canadian passports.
They insisted that such reports were part of a campaign of "psychological warfare" against Iran being led by the United States.
The Guards' top commander, Hossein Salami, said "we are more upset than anyone over the incident", state media reported.
Trudeau said the admission of guilt is a positive sign Iran will "fully allow a credible, independent global investigation".
Iran's Supreme Leader Ali Khamenei has banned direct talks with the U.S. We are following your protests closely, and are inspired by your courage. "Thousands have already been killed or imprisoned by you, and the World is watching", Trump tweeted in a post that was also translated to Farsi. He was accused of "inciting, quot; protesters in front of Amir Kabir University on Saturday". "It can continue its march towards pariah status with all the political and economic isolation that it entails, or take measures to reduce tensions and take a diplomatic path forward". That missile attack came in retaliation for the death of Iranian Gen. Qasem Soleimani, who was killed by an American drone strike near Baghdad on January 3.
Tensions with the United States eased after the ballistic missile attack, when Trump declined to respond and welcomed Iran's apparent decision to stand down.
It also raised a host of new questions, such as why Iran did not shut down its global airport or airspace on Wednesday when it was bracing for the U.S.to retaliate for a ballistic missile attack on two military bases housing US troops in Iraq. "This is a crime against humanity", said exiled Persian Crown Prince Reza Pahlavi on Saturday. "Khamenei and his regime should go". In some of the clips, protesters can be heard chanting anti-government slogans. His father died in exile in 1980.
"Either the "jamming" system was the cause or the network was busy or whatever, he couldn't get in touch", said the Iranian general.
Soleimani's funeral had prompted huge public gatherings, which the authorities described a show of national unity. But those displays of emotion have been overshadowed as protesters on Saturday tore up pictures of the slain general. "The support base for the Islamic Republic is getting smaller and more segments of Iran's population are questioning the legitimacy of its leaders - but nevertheless the support for the ruling elite remains powerful enough (no matter its shrinking size) to maintain its survival".
However, he attributed the incident to human error while apologizing to the citizens and families of the victims.