The French government says the United States should expect "united and strong" retaliation from European countries if it moves to impose more tariffs.
"If tomorrow there is an increase in tariffs, like in the car industry, our reaction should be united and strong to show that Europe is a united and sovereign power," French Finance Minister Bruno Le Maire said in an address to an economic conference in Aix-en-Provence, southern France, on Sunday.
"The question is no longer whether or not there will be a trade war, the war has already started," he added.
"Let it be known that if we are attacked we will react collectively and we will react firmly," Le Maire said.
On June 10, the administration of US President Donald Trump imposed 10 percent tariffs on aluminum imports and 25 percent tariffs on steel imports, which mainly affects the EU, Canada, and Mexico, ending exemptions that had been in place since March.
Trump argued at the time that enormous flows of imports to the US were putting in jeopardy the American national security, and made an odd departure from a decades-long US-led move towards open and free trade.
He further escalated tensions last month with threats to impose up to 20 percent tariffs on all cars and car parts manufactured within the EU, a move that could upend the industry's current business model for selling cars in the US.
German Chancellor Angela Merkel, whose country is facing the threat of higher US duties, said on Thursday that she may support an initiative to reduce European Union tariffs on US car imports as the bloc seeks to avoid more levies on its car exports.
Merkel said the door was open for negotiations on how to handle tariffs with the US so that the EU could avoid a further deterioration of trade relations with Washington under President Trump.
The United States currently imposes a 2.5 percent tariff on imported passenger cars from the 28-nation EU and a 25 percent tariff on imported pickup trucks.
The EU has introduced tariffs of 25 percent on a range of US goods to compensate for Trump’s controversial tariffs on European metals. The bloc imposes a 10 percent tariff on imported US cars.
According to World Trade Organization rules, the EU cannot reduce import tariffs for only US-made cars but for all WTO members.
The European Union on Monday warned Washington that imposing import tariffs on cars from the bloc could lead to “countermeasures” against nearly $300 billion worth of US exports.
