Democratic presidential nominee Joe Biden has warned the UK against breaking the Brexit deal, saying he will not allow peace in Northern Ireland to become a "casualty" if he is elected in November, the media reported.

Taking to Twitter on Wednesday, Biden said: "We can't allow the Good Friday Agreement that brought peace to Northern Ireland to become a casualty of Brexit.

"Any trade deal between the US and UK must be contingent upon respect for the Agreement and preventing the return of a hard border. Period."

The Good Friday Agreement refers to a pair of deals signed on April 1998 that ended most of the violence of the Troubles, a political conflict in Northern Ireland that had been ongoing since the 1960s.

It served as a major development in the Northern Ireland peace process of the 1990s.

His tweet comes as visiting UK Foreign Secretary Dominic Raab has been trying to reassure US politicians about the latest Brexit developments, the BBC reported.

While Secretary of State Mike Pompeo said he trusted the UK to "get this right", House Speaker Nancy Pelosi said there was "no chance" of a UK-US trade deal getting through Congress if Britain violated international agreements.

Brexit is high on the agenda at Raab's Washington meetings, after the controversial Internal Market Bill, which would give the UK government the power to override part of the Brexit withdrawal deal, cleared its first Parliamentary hurdle earlier this week.

It now faces further scrutiny in the House of Commons, and also needs to be passed by the House of Lords.

If the law comes into force, it would breach international law, reports the BBC.

On Tuesday, four US Congressmen in a letter to UK Prime Minister Boris Johnson said the plans to give ministers powers to override part of the UK's exit agreement, designed to avoid a hard Irish border. could have "disastrous consequences for the Good Friday Agreement and broader process to maintain peace on the island of Ireland"..