Canada has closed its embassy in Tehran and ordered the expulsion of Iranian diplomats from Ottawa, partly because of the country's backing of the Syrian regime.

Canada's foreign affairs minister, John Baird, cited Iran's support for Bashar al-Assad, its disputed nuclear programme and continued human rights violations as reasons behind his country's decision to sever diplomatic ties with Tehran. He said the Canadian government perceived Iran to be "the most significant threat to global peace and security in the world today". "Canada has closed its embassy in Iran, effective immediately, and declared personae non gratae all remaining Iranian diplomats in Canada," Baird said.

All Canadian diplomatic staff had left Iran and Iranian diplomats in Ottawa had five days to leave the country. Canada joins its main allies, the US and the UK, as countries without diplomatic presence in Tehran.

"The Iranian regime is providing increasing military assistance to the Assad regime; it refuses to comply with UN resolutions pertaining to its nuclear programme; it routinely threatens the existence of Israel and engages in racist anti-Semitic rhetoric and incitement to genocide," Baird said in the statement published on Canada's government website for foreign affairs and international trade.

Ottawa's move comes only a week after Iran attempted to seize upon an international conference in Tehran to claim a diplomatic triumph in defiance of western-led efforts to isolate the regime. To the dismay of Iran, two of its main guests for Tehran's summit of the Non-Aligned Movement, the UN secretary general, Ban Ki-moon, and Egypt's president, Mohamed Morsi, embarrassed the host by making speeches unwelcome by the regime. Morsi, in particular, stunned Iran, a staunch supporter of Assad, with a plea to the world to back Syrian rebels.

Canada is an outspoken critic of Iran's human rights record and has actively pursued the effort to hold Tehran leaders accountable for their right's violations on international platforms in recent years, including through sanctions.

Baird said: "[Iran] is among the world's worst violators of human rights; and it shelters and materially supports terrorist groups, requiring the government of Canada to formally list Iran as a state sponsor of terrorism under the Justice for Victims of Terrorism Act. Moreover, the Iranian regime has shown blatant disregard for the Vienna convention and its guarantee of protection for diplomatic personnel. Under the circumstances, Canada can no longer maintain a diplomatic presence in Iran.Our diplomats serve Canada as civilians, and their safety is our number one priority."

Baird appeared to be referring to an incident last November when protesters in the Iranian capital stormed the British embassy in Tehran, ransacking offices and diplomatic residence.

Payam Akhavan, a professor of international law at McGill University in Montreal, said the recent row was the worst crisis in bilateral relations between Tehran and Ottawa for many years.

"I think the closure of Iranian embassy in Ottawa should be seen in the context of concerns by the Canadian government about the Islamic republic's recent activities in its Ottawa mission, including using it to establish wider presence in Canada through a series of ostensibly cultural activities, at universities and other institutes and infiltrating the Iranian diaspora and neutralising opposition to the regime," he said.

According to latest official figures more than 400,000 Iranians live in Canada. "There is an significant Iranian diaspora in Canada, we call Toronto, Tehranto, even many regime insiders live here but the majority consists of refugees or migrants," said Akhavan.

The Canadian embassy in Ankara, Turkey, will provide services to Canadians living in Iran in the absence of Tehran's mission. The Canadian foreign ministry has also upgraded its Iran travel advice, urging all its citizens not to travel to Iran.

"Canadians who have Iranian nationality are warned in particular that the Iranian regime does not recognise the principle of dual nationality," it said. "By doing so, Iran makes it virtually impossible for government of Canada officials to provide consular assistance to Iranian-Canadians in difficulty."

The frosty relations between the two capitals became even more restrained in 2003 when an Iranian-Canadian photographer, Zahra Kazemi, died while in jail in Iran. Iran said she died of a stroke but Canada insisted she died under torture because of a skull fracture.

A number of Iranian-Canadians are currently held behind bars in Iran, including Hamid Ghassemi-Shall who is facing execution after being convicted of espionage, a charge his family say is trumped-up.

There was no immediate reaction from Iran in response to Canada's move but Iranian state news agencies reported Baird's statement.