Donald Trump has threatened the European Union over what he perceives as “brutal” treatment from the bloc in its approach to Brexit and trade dealings with the US.

“Too bad that the European Union is being so tough on the United Kingdom and Brexit,” Mr Trump tweeted late on Wednesday. “The EU is likewise a brutal trading partner with the United States, which will change.

“Sometimes in life you have to let people breathe before it all comes back to bite you!”

The US president’s complaint came hours after EU leaders agreed to a lengthy Article 50 extension, allowing Britain to remain a member state until 31 October and giving Theresa May more time to get a withdrawal deal through parliament.

It is unclear which elements of the EU’s Brexit negotiation strategy the president believes to be unfair, but he has long railed against the bloc’s trade policies, and on Tuesday announced the US would impose tariffs on $11bn (£8.4bn) of EU goods, including cheddar cheese, aeroplane components and motorbikes.

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“The World Trade Organisation finds that the European Union subsidies to Airbus has adversely impacted the United States, which will now put Tariffs on $11bn of EU products!” he tweeted.

“The EU has taken advantage of the US on trade for many years. It will soon stop!”

In fact, the WTO has handed down unfavourable rulings to both the EU and US in recent months. In March, it ruled Washington had failed to stop giving Boeing illegal tax subsidies, and last year issued a similar ruling against EU subsidies to Airbus.

Mr Trump’s late-night tweet on Wednesday came just minutes after he stepped up his attacks on the Democratic Party by baselessly accusing it of treason, a crime punishable by death in the US.