A trade war is now a reality, French Finance Minister Bruno Le Maire has warned as G20 ministers gather for a summit in Argentina.
The current US trade policy of imposing unilateral tariffs is based on "the law of the jungle", he said.
But US Treasury Secretary Steven Mnuchin defended the tariffs and urged the EU and China to open their markets to allow free competition.
Last week, US President Donald Trump described the EU as a foe on trade.
Mr Trump later threatened to impose tariffs on all $500bn (£380bn) of Chinese goods entering the US in a growing trade row.
The US has large trade deficits with both the 28-member EU and China.
The two-day talks in Buenos Aires bring together finance ministers and central bankers of the world's top 20 economies.
How has the tariffs row worsened?
On June 1, the Trump administration introduced tariffs of 25% on steel and 10% on aluminium imported into the US.
Mr Trump argues that global oversupply of steel and aluminium, driven by China, threatens American producers, which are vital to the US.
The US president believes that if you have a trade deficit - if you import more than you export - you are losing out.
The EU later introduced retaliatory tariffs on a range of US goods, including bourbon whiskey, Harley Davidson motorcycles and orange juice.
On China, Mr Trump warned earlier this week he was ready to slap tariffs on all imports from the country.
Last week, Washington listed $200bn worth of additional Chinese products it intends to place tariffs on as soon as September.
The list named more than 6,000 items including food products, minerals and consumer goods such as handbags, to be subject to a 10% tariff.
It is still under public consultation, to last until the end of August.
The US and China have already imposed tit-for-tat tariffs of $34bn on each other's goods.