Speaking during an interview with German broadcaster ZDF on Tuesday, Mr Johnson said: “If Putin were a woman, I just don’t think he would have started such a macho war.”
“If you want a very good example of toxic masculinity, he’s got that in front of us,” he added, according to the outlet’s translation.
Toxic masculinity is a term that refers to traditional sterotypes surrounding men, and the harm those qualities can inflict on society. Traits often considered under the umbrella term include, but are not restricted to, misogyny and homophobia, and the promotion and normalising of violence or violent behaviours.
Putin’s war, which has been raging in the eastern European country for more than four months, was launched on 24 February, and is referred to by Moscow as a “special military operation” organised to “denazify” Ukraine.
Mr Johnson’s comments come after a Russian missile strike a Ukrainian shopping mall killed at least 18 people, while another 36 are still missing.
The attack, in the central city of Kremenchuk – far from any frontline – drew a wave of global condemnation, with France’s Emmanuel Macron among leaders who called it a “war crime”.
Ukraine said Moscow had killed civilians deliberately. Russia said it had struck an arms depot and falsely claimed the mall was empty.
And with no sign of the war letting up, Nato members announced they would instal 300,000 troops at high readiness – up from the current 40,000 – and the UK will commit capabilities in land, air and sea to the “new force model”.
Mr Johnson told reporters: “We’ve already got in Estonia a very significant enhanced forward presence of two battlegroups.
“We’re working with premier Kaja Kallas on what we can do to be more supportive to to Estonia, to help them operationally.
“The work is is going on for a close political and military partnership. Our commitment to Estonia, like our commitment to all our Nato friends, is absolute.”
Alliance members have also committed to spending at least 2 per cent of gross domestic product (GDP) – a measure of the size of the economy – on defence, but only nine of the 30-member alliance meet that requirement.
Mr Johnson claims the UK will spend 2.3 per cent this year and will push for allies to do more.
He said: “The Nato alliance keeps our people safe every day. But over the next 10 years the threats around us are only going to grow.
“We need allies – all allies – to dig deep to restore deterrence and ensure defence in the decade ahead.
“The 2 per cent was always meant to be a floor, not a ceiling, and allies must continue to step up in this time of crisis.”