Rescue teams work amid plane parts and debris at the crash site outside of Tehran. Photo: AFP via Getty Images

The passenger jet, Flight PS752, turned farmland into fields of flaming debris.

Ukrainian Foreign Affairs Minister Vadym Prystaiko said 82 Iranians, 63 Canadians and 11 Ukrainians were on board — the Ukrainian nationals included two passengers and the nine crew. There were also 10 Swedish, four Afghan, three German and three British nationals, he said.

Transport Minister Marc Garneau said Canada was offering technical assistance to the impending investigation.

Prime Minister Justin Trudeau said he was "shocked and saddened," and he and his wife, Sophie, extended their condolences to those who lost loved ones.

"Our government will continue to work closely with its international partners to ensure that this crash is thoroughly investigated, and that Canadians' questions are answered," said Trudeau.

"Today, I assure all Canadians that their safety and security is our top priority. We also join with the other countries who are mourning the loss of citizens."

François-Philippe Champagne, Canada's minister of foreign affairs, said he was in touch with the Ukrainian government.

Champagne said in a statement Wednesday afternoon that "the situation remains extremely fluid" with respect to the number of Canadian fatalities.

"As more information becomes available, including regarding dual citizens, this number could change," he said.

The statement included contact information of the Global Affairs Canada's Emergency Watch and Response Centre for those concerned about friends and relatives who may have been on the flight.

The crash came hours after Iran launched a ballistic missile attack on Iraqi bases housing U.S. soldiers, but Iranian officials said they suspected a mechanical issue brought down the 3½-year-old Boeing 737-800 aircraft. Ukrainian officials initially concurred, but later backed away and declined to offer a cause.