Trump's tweet came a day after Britain's International Trade Secretary Liam Fox met with US Trade Representative Robert Lighthizer in Washington.
The two countries are currently discussing a potential for a bilateral trade deal after Britain's withdrawal from the EU in March, 2019.
"Working on major Trade Deal with the UK. Could be very big and exciting. Jobs! The EU is very protectionist with the US. Stop!" Trump said in a tweet to his more than 34.4 million followers on this social media website.
Trump has been a supporter of bilateral trade deal and opposed to multilateral trade agreements.
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The bilateral trade between the two countries is said to be around USD 200 billion.
Currently in Washington, Fox also met US Vice President Mike Pence.
Writing in The Wall Street Journal, Fox said he is looking forward to a new era of trade with the US once the UK leaves EU.
"As an independent UK embraces the world, the US will remain our foremost partner," he said.
"As the UK prepares to leave the European Union, Britain enters a new chapter in our history," Fox told a Washington audience at the American Enterprise Institute.
Fox gave the example of India of how it adopted globalisation and liberalisation to fight the increasing poverty.
"Take India as an example. In 1993, around 45 per cent of India's population sat below the poverty line, as defined by the World Bank. In 2011 it was 22 per cent," he said.
"It is no coincidence that in the intervening period India embraced globalisation and started to liberalise its economy. It is hard to imagine an international aid programme, even one as generous as our own, that would, or could, have ever been as effective," Fox said.