The reality of a trade war has arrived, according to Bruno Le Maire, the French finance minister, speaking as G20 ministers gathered for a summit in Argentina.

He said the US trade policy of unilateral tariffs was based on the "law of the jungle" as he pushed back against the demands of Donald Trump's administration.

The result is that the US and its European Union allies are locked in trade stalemate after Steven Mnuchin, US Treasury Secretary, refused to drop US demands.

In his opening salvo at the Group of 20 summit in Buenos Aires, Mr Mnuchin urged China and the EU to respect "free, fair and reciprocal trade" amid talk of an escalating global trade conflict, but his French counterpart fired back that the US must "return to reason."

Mr Mnuchin was inflexible in his approach to the EU following a series of tit-for-tat measures that began with US President Donald Trump's decision to slap tariffs on steel and aluminum imports.