Donald Trump has repeated his threat to introduce tariffs on European car imports, on the day EU reprisals against US steel levies came into force.
The US president used his favoured mode of communication - Twitter - to threaten an escalation that would add 20% duty on vehicles entering America.
It is the latest twist in the row between the United States and EU countries including Britain over trade tariffs on metal imports to the US.
Mr Trump tweeted on Friday afternoon: "Based on the Tariffs and Trade Barriers long placed on the U.S. and it (sic) great companies and workers by the European Union, if these Tariffs and Barriers are not soon broken down and removed, we will be placing a 20% Tariff on all of their cars coming into the U.S. Build them here!"
Around £2.4 billion worth of US products including bourbon, peanut butter, cranberries and orange juice were hit with increased tariffs from Friday.
It followed Mr Trump's decision in May to hit steel and aluminium imports with tariffs of 25% and 10% respectively, sparking fears of a trade war.
Earlier this month, at a bad-tempered G7 summit in Canada, Mr Trump accused other states of "robbing" his country through their trade policies and proposed scrapping tariffs across the G7.
Responding to the EU tariffs before the tweet, shadow international development secretary Barry Gardiner said: "Donald Trump said he would welcome a trade war and could win it, but the workers in the motorbike factories in Wisconsin, Missouri and Pennsylvania are the foot soldiers he is prepared to sacrifice.
"Nobody wins in a trade war and Donald Trump may finally come to realise that his attack on steel workers in Europe was not such a good idea after all, as the European Union is forced to reciprocate with retaliatory tariffs.
"We don't want to see a trade war and, ultimately, these tariffs need to be removed by both sides as we begin to work together to address the real issue of global overcapacity in steel and unfair market practices."