The Prime Minister said no Nato countries are contemplating becoming actively involved in repelling Moscow’s invasion, with Ukraine not being a member of the defence alliance.
Ms Truss said over the weekend that she would “absolutely” support British nationals who chose to join the fight, with a number of Britons keen to fight against Vladimir Putin.
But that advice runs contrary to the Foreign Office advice against all travel to Ukraine, and Mr Johnson became the latest Cabinet minister to warn Britons away.
A journalist in Estonia suggested that the UK Government was supporting volunteers in their endeavours, but the Prime Minister replied: “I’m going to be very clear about this because you’re not quite right in what you say about supporting volunteers going to fight, the UK is not actively doing such a thing.
“But I understand of course the feelings of people who feel emotionally engaged in this conflict because I cannot think of a time in international affairs when the difference between right and wrong, between good and evil, has been so obvious.
“I can understand why people feel as they do but we have laws in our country about international conflicts and how they must be conducted.
“Nato is a defensive alliance.
“I think for any Nato member to get involved actively in conflict with Russia is a huge step which is not being contemplated by any member.”