Speaking to the BBC in a new documentary titled Putin Vs. the West, Johnson recalled the “extraordinary” conversation he shared with the Russian President during a “very long” phone call in February 2022.

“He threatened me at one point, he said, ‘Boris, I don’t want to hurt you but, with a missile, it would only take a minute,’ or something like that,” Johnson said.

It is impossible to tell whether Putin’s alleged threats to the then British leader were legitimate. However, Johnson speculated that the threat was empty.

“I think from the very relaxed tone that he was taking, the sort of air of detachment that he seemed to have, he was just playing along with my attempts to get him to negotiate,” he told the BBC.

Representatives for the Russian government did not respond to Fortune’s questions about Johnson’s allegations.

Any threat Putin did make to Johnson would not have been an isolated incident, however. In September, Putin said Russia possessed “various means of destruction” and “lots of weapons to reply” to what he called Western aggression. He warned that Moscow would “certainly use all the means at our disposal” to respond to any perceived threats.

“I’m not bluffing,” he insisted in a televised address.

Invasion prologue

In early 2022, the U.S. and its allies warned that an invasion of Ukraine by Russia was imminent as Moscow amassed up to 190,000 troops at its Ukrainian border and carried out a series of huge military drills.

At the time, Russia denied allegations it was about to invade its neighbor. Its forces invaded Ukraine on Feb. 24.

It came after Russia invaded and annexed Crimea, a peninsula in southern Ukraine, in 2014, which marked the beginning of the war between the two countries that would be ramped up with the wider invasion in 2022.

In a bid to convince Moscow to stand down in the run-up to last year’s invasion, a number of world leaders—including U.S. President Joe Biden, French President Emmanuel Macron and German Chancellor Olaf Scholz—held in-person or telephone talks with the Kremlin in the first two months of last year.

Johnson told the BBC documentary, which is investigating Putin’s interactions with other world leaders, that he had warned the Russian President a wide-scale war in Ukraine would be an “utter catastrophe.”

The former prime minister, who resigned from office in July but was leading the U.K. government when Moscow launched its full-scale assault on Ukraine, described Putin’s tone during the call as “very familiar.”

Despite Johnson’s assumption that Putin’s threats were merely a negotiation tactic, Russia has, in recent years, been accused of carrying out a state-backed attack in the United Kingdom.

Anglo-Russian relations were tested in 2018 when the Kremlin was accused of orchestrating the poisoning of a former Russian spy on British soil. Sergei Skripal and his daughter Yulia were poisoned with the military-grade nerve agent Novichok in the English city of Salisbury. Both survived, but a local woman died after inadvertently coming into contact with the discarded nerve agent.

Russia denied any involvement in the poisonings, with the suspects in the case claiming they were just tourists and Putin himself saying there was “nothing criminal” about the two men.