After three years spent trying to deter Russia from destroying Ukraine, European Union leaders grappled on Monday with how to respond to a major ally who appears determined to start a trade war or even seize part of their territory.

Shares in Europe and Asia have fallen after US President Donald Trump announced tariffs on Canada, Mexico and China, and said tariffs on the EU would "definitely happen". The German and French stock markets were down about 2%, with shares in carmakers among the worst hit, while London's FTSE 100 dropped more 1%.