"My message is pretty clear, it's the same message the President delivered at the G-7: If Europe believes in free trade, we're ready to sign a free trade agreement with no tariffs, no non-tariff barriers and no subsidies. It has to be all three," said Mr Mnuchin.
That brought a firm response from France's Finance and Economy Minister Bruno Le Maire at the G-20 meeting, which brings together finance ministers and central bank governors from the world's 20 leading economies.
He said he expected "a change of attitude" from Mr Trump, otherwise "there will be no choice other than to retaliate".
International Monetary Fund chief Christine Lagarde opened the summit by reiterating her fears that increasing trade restrictions would hurt global gross domestic product.
But Mr Mnuchin showed no signs of a US willingness to back down.
