Britain and France are "not ruling out" deploying their troops on the ground in Ukraine over fears Donald Trump could withdraw American military aid when he re-enters the White House in January.
Talks over sending British and French troops to help their Ukrainian counterparts are said to have been "reactivated" after France's suggestions earlier this year were shot down.
But with a second Trump presidency fewer than two months away, Western Europe's two nuclear powers have begun to reconsider.
"Discussions are underway between the UK and France regarding defence cooperation, particularly with the aim of creating a core of allies in Europe, focused on Ukraine and broader European security," a British military source told French outlet Le Monde.
Western Europe's two nuclear powers have begun to reconsider their red lines
PA
French ministers have vowed to 'support Ukraine as intensely and as long as necessary'
REUTERS
But on the other side of the Atlantic, Trump's team have distanced themselves from sending US personnel to Ukraine.
One ally of the President-elect told the Wall Street Journal: "We can do training and other support, but the barrel of the gun is going to be European.
"We are not sending American men and women to uphold peace in Ukraine. And we are not paying for it. Get the Poles, Germans, British and French to do it."
However, Nato bigwigs have warned that there will be no "just peace" in Ukraine without American boots on the ground.
China, Iran and North Korea have been accused of 'standing openly beside Putin'
REUTERS
Last week, Estonian Foreign Minister Margus Tsahkna told the Financial Times: "If we are talking about real security guarantees, it means that there will be a just peace.
"Then we are talking about Nato membership. But without the US, it is impossible. And then we are talking about any form [of guarantee] in the meaning of boots on the ground."
Any US involvement would doubtless only heighten warnings that "World War Three has already begun".
Just days ago, Ukraine's former military chief said a Third World War was already underway with China, Iran and North Korea "standing openly beside Putin".