About seven vehicles were deployed outside the studio in Chiswick Park, west London, after “severe and credible” threats were recently made against two of the channel's journalists, a company spokesmen said.
The deployment on Saturday came as Canada's spy agency warned it was investigating “credible” death threats from Iran, and three days after the UK’s MI5 intelligence chief said that Iran wanted to kidnap or kill Britons that it sees as “enemies of the regime”.
London’s Metropolitan Police said officers “are working in response to potential threats projected from Iran against a number of UK-based individuals.
“Whilst we will not be going into detail as to what these are, it does include the presence of overt armed police officers in the vicinity of the west London offices of a UK-based Persian language media company,” the force said.
Iran International is an independent UK-based Farsi-language news channel, which has been highly critical of the Iranian government.
It has also covered the widespread protests in Iran after the death of Mahsa Amini in police custody in Tehran in September
The channel has been proscribed as a “terrorist” organisation by Iran, but it can still be accessed via the internet.
“The threats against us have escalated as the protests in Iran go on, because we cover them 24/7,” said the media outlet's spokesman.
He said the presence of armed vehicles was a “massive deterrence” that had “reassured” staff.
“They've worked there for five years, they're used to this, their families get threatened in Iran,” he said.
“Recently in Tehran there have been wanted posters going up with some of our presenters' faces on them. But the mood is just getting on with it.”
MI5 Director general Ken McCallum said on Wednesday that Iran wants to kidnap or kill UK-based individuals it deems “enemies of the regime”, with at least 10 such plots uncovered so far this year.
Mr McCallum warned in a speech at the agency's Thames House headquarters that Iran “projects threat to the UK directly, through its aggressive intelligence services”.
He said this could include “ambitions to kidnap or even kill British or UK-based individuals perceived as enemies of the regime”.
Last week, Foreign Secretary James Cleverly summoned Iran's top-ranking diplomat in London, accusing Tehran of threatening the lives of UK-based journalists.
Canada's spy agency said on Friday it was investigating reports from people living in the country who have received “credible” death threats from Iran, the Canadian Security Intelligence Service (CSIS) said.
The threats are “designed to silence those who speak out publicly” against Iran, the statement said.
CSIS is collecting information from people who experienced harassment and intimidation linked to the Islamic Republic of Iran, the statement said.
“CSIS is actively investigating several threats to life emanating from the Islamic Republic of Iran based on credible intelligence.”
The agency is working closely with Iranian-Canadian communities which have been “disproportionately” targeted, the statement said.