Donald Trump has told Britons that he supports Brexit, repeating just days before the vote on June 23 that he thinks the UK would be better off outside the European Union.

As the campaign to decide Britain's EU membership restarted after a three-day hiatus following the killing of lawmaker Jo Cox, Trump, the presumptive Republican U.S. presidential candidate, said in a newspaper interview he was backing an "out" vote.

"I would personally be more inclined to leave, for a lot of reasons like having a lot less bureaucracy," he told the Sunday Times. "But I am not a British citizen. This is just my opinion."

The billionaire businessman also told the newspaper that he would seek to have good relationships internationally if he were elected president in November, including with David Cameron. The British Prime Minister has in the past called Trump's proposed temporary ban on Muslims entering the United States "divisive, stupid and wrong".

Trump said in May that Britain would be better off outside the EU because of high levels of migration.

The latest opinion polls showed the 'Remain' camp recovering some momentum, although the overall picture remains one of an evenly split electorate.

Trump, whose mother was Scottish, is due to be in Britain the day after the referendum, when he visits two golf courses he owns in Scotland.

Trump also said that if he became president he would try to improve the trade deals the U.S. has with China, and work more closely with Russia and that could include co-operating with Russia in the fight against Islamic State.