President Vladimir Putin threatened to personally target Boris Johnson with a missile attack just before ordering Russian forces into Ukraine, the former UK prime minister has claimed.

The apparent threat came in a phone call just ahead of the invasion on February 24, according to a new BBC documentary to be broadcast on Monday.

Johnson and other Western leaders had been hurrying to Kyiv to show support for Ukraine and try to deter a Russian attack.

"He sort of threatened me at one point and said, 'Boris, I don't want to hurt you, but with a missile, it would only take a minute', or something like that," Johnson quoted Putin as saying.

Johnson emerged as one of the most impassioned Western backers of Ukrainian President Volodymyr Zelensky.

But prior to the invasion, he says he was at pains to tell Putin that there was no imminent prospect of Ukraine joining NATO, while warning him that any invasion would mean "more NATO, not less NATO" on Russia's borders.

"He said, 'Boris, you say that Ukraine is not going to join NATO any time soon.

"'What is any time soon?' And I said, ‘well it's not going to join NATO for the foreseeable future. You know that perfectly well'."

On the missile threat, Johnson added: "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."

The BBC documentary charts the growing divide between the Russian leader and the West in the years before the invasion of Ukraine.

It also features Zelensky reflecting on his thwarted ambitions to join NATO prior to Russia's attack.

"If you know that tomorrow Russia will occupy Ukraine, why don't you give me something today I can stop it with?" he says.

"Or if you can't give it to me, then stop it yourself."