British Foreign Secretary Boris Johnson said on Monday he was sure that Britain and the United States could conclude a free trade deal that was in their mutual interests after President-elect Donald Trump said he was keen for one.

"It's very good news that the United States of America wants to do a good free trade deal with us and wants to do it very fast and it's great to hear that from President-elect Donald Trump," Johnson told reporters as he arrived at a meeting of EU foreign ministers in Brussels.

"Clearly it'll have to be a deal that's very much in the interests of both sides but I've no doubt that it will be."

In a newspaper interview, Trump welcomed Britain's decision to leave the European Union, a move which could give it the opportunity to conclude bilateral trade agreements.