Iran considers dual nationals aboard a Ukrainian plane that was shot down accidentally this month to be Iranian citizens, a Foreign Ministry spokesperson said on Monday.

Iran does not recognize dual nationality. Many of the 176 people killed in the disaster were Iranians with dual citizenship. Canada had 57 citizens on board.

"We have informed Canada that Tehran considers dual nationals who were killed in the plane crash as Iranian citizens … Iran is mourning their deaths," Foreign Ministry spokesperson Abbas Mousavi told a televised weekly news conference.

Mousavi announced that the "loved ones who have perished were Iranian" and that Iran did not accept their dual citizenships.

"According to our laws … we recognize them as Iranians. We will take measures for the victims and their families according to our own laws," he said.

In his speech, Mousavi also criticized Canada for following diplomatic pressures imposed by United States, saying Iran had announced its "readiness to have a consular section" but the requests had been ignored by the Canadian government.

"Yet they don't even allow hundreds of thousands of Iranians who are in Canada to use basic consular services …. And now, in this type of situation, they are worried about Iranians."

British ambassador briefly detained

Under Prime Minister Stephen Harper, the federal government cut diplomatic ties with Iran in 2012. The Liberals pledged to re-engage with the country in 2015, but to date, bilateral relations have not been renewed.

As protests erupted in Iran over the plane disaster, the British ambassador in Tehran was briefly detained. Officials said he was at an "illegal" rally, while the envoy said he was attending a vigil for victims. Britain criticized his detention.

"Iran respects all foreign diplomats in Iran as long as they do not violate international laws," Mousavi said.

Spokesman for Iran's foreign ministry Abbas Mousavi, seen in this file photo, said Monday that Iran does not recognize dual nationality of those killed in the downing of Ukraine International Airlines Flight PS752. (Atta Kenare/AFP/Getty Images)

Aurel Braun, professor of international relations and political science at the University of Toronto's Munk School of Global Affairs, said Iran's statement was tantamount to denying the Canadian citizenship of those killed.

"It complicates co-operation [with Canada] when recovering remains and investigating the crash. It just makes everything vastly more difficult," Braun told CBC News.

Refusing to acknowledge dual citizenship was a "matter of control," and a signal to those travelling the country that they are subject to the "whims of the totality of the regime's power," he said.

"It is a fear of external interference."

Foreign Affairs Minister François-Philippe Champagne's office told CBC News that Canada has had assurance from Iran that the deceased families' wishes would be respected regarding where remains would go.

"We continue to expect that that will be the case and have been clear with the Iranians about that expectation," spokesperson Adam Austen said.

Ukraine wants black boxes

Also on Monday, Ukraine urged Iran to return the black boxes from the downed plane.

Ukrainian Foreign Minister Vadym Prystaiko said returning the boxes would show that Iran was committed to an unbiased investigation.

Prystaiko was speaking as an Iranian delegation led by Minister of Roads and Urban Development Mohammad Eslami was visiting Kyiv to discuss the Jan. 8 tragedy.

"His main task is to apologize and acknowledge what happened. We hope that we can go a little further than just political discussions and discuss practical problems. Among them in particular is the return of the black boxes," Prystaiko told reporters.

Iran said on Sunday it was trying to analyze the black boxes, denying an earlier report it would give them to Ukraine.

"At first they stated that they were handing them over, then the same person stated that they were not handing them over. This created some misunderstanding in Ukraine and we were starting to be asked: are they being handed over or not?"

The office of President Volodymyr Zelensky said Iranian experts were expected to assess Ukraine's technical ability to decode the black boxes. A statement said the wreckage of the aircraft was to be returned to Ukraine.

"I promised the families and relatives of the victims, I promised the people of Ukraine that the truth will be established. We must know what happened," the statement quoted Zelensky as telling the Iranian minister.