With Russian forces bearing down on Kiev, President Volodymyr Zelensky has announced the formation of a new “international legion” to help defend his country.
He has appealed to foreign volunteers to come forward promising them arms to fight against the invading army.
Asked on the BBC’s Sunday Morning programme if she would support UK citizens who chose to answer the call, Ms Truss said: “That is something people can make their own decisions about.
“Absolutely, if people want to support that struggle I would support them in doing that.”
Mr Zelensky’s call for an international legion carried echoes of the International Brigade which fought against the fascists – backed by Nazi Germany – in the Spanish Civil War in the 1930s.
Ukrainian foreign minister Dmytro Kuleba appeared to encourage the comparison, saying that just as Hitler had finally been defeated “we will defeat Putin, too”.
“Foreigners willing to defend Ukraine and world order as part of the International Legion of Territorial Defense of Ukraine, I invite you to contact foreign diplomatic missions of Ukraine in your respective countries,” he tweeted.
“Together we defeated Hitler, and we will defeat Putin, too.”
There have in the past been questions about the legality of Britons going abroad to fight in foreign conflicts.
In 2014, the Crown Prosecution Service warned that UK nationals who went to fight in the Syrian civil war could be committing an offence, even if they joined the rebels fighting to overthrow President Bashar Assad.