Joe Biden warned Boris Johnson against his Brexit plans during his first calls to world leaders

• Joe Biden used his first phone call with Boris Johnson as President-elect to issue a warning against Boris Johnson's Brexit plans.
• The President-elect raised the Good Friday Agreement, which senior Democrats have warned could be undermined by Johnson's plans.
• The move will compound concerns that Boris Johnson's Brexit policy could create tensions between the UK and US.
• According to the Financial Times, Biden was firm on the issue of Brexit and brought up the subject twice in relation to Northern Ireland.
• Biden has previously stated that Brexit legislation Johnson is trying to push though parliament could undermine peace arrangements in Northern Ireland.
• "We can't allow the Good Friday Agreement that brought peace to Northern Ireland to become a casualty of Brexit," Biden wrote in a tweet in September.

Joe Biden used his first phone call with Boris Johnson as President-elect to put more pressure on the prime minister about his Brexit plans.

Biden on Monday began calling world leaders including French President Emmanuel Macron, German Chancellor Angela Merkel, Irish President Micheál Martin, and UK Prime Minister Boris Johnson.

A read-out from the Biden transition team on Monday said that the pair discussed issues including climate change and the Covid-19 pandemic while Biden "reaffirmed his support for the Good Friday Agreement."

According to the Financial Times, Biden was firm on the issue of Brexit and brought up the subject twice in relation to Northern Ireland, warning that the UK's exit plans must not impede the Good Friday Agreement, the landmark peace deal which largely brought peace to the island of Ireland.

A Downing Street spokesman told Business Insider on Wednesday: "They had a very positive call. What they talked about was the importance of implementing Brexit in such a way that upholds the Good Friday Agreement and the prime minister assured the president-elect that would be the case."

The call came after Johnson tweeted a message congratulating Biden, which contained remnants of an earlier version which instead falsely congratulated Trump on winning a second term. Johnson's spokesman blamed a "technical error" for the gaffe.

Business Insider has previously reported that the Biden camp holds strong reservations about Johnson personally — especially given Biden's opposition to Brexit. However, the call has been welcomed by Downing Street as an indication that the President-elect intends to build a strong and pragmatic relationship with the UK.

Biden has previously stated that Brexit legislation Johnson is trying to push though parliament could undermine peace arrangements in Northern Ireland. He warned in September that he would refuse to agree a trade deal with the UK if Boris Johnson followed through on British legislation which he said could undermine peace in Northern Ireland.

"We can't allow the Good Friday Agreement that brought peace to Northern Ireland to become a casualty of Brexit," Biden wrote in a tweet dated September.

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

The president-elect's concerns relate to the Internal Market Bill, which ministers in Johnson's government have admitted will create what they called a "limited" breach of international law. The legislation relates to the passage of goods between Northern Ireland and the rest of the UK, and critics say it could see the reimposition of a hard border, although Downing Streets insists the bill designed to protect the Good Friday Agreement.

Johnson this week pushed on with his bid to put the law onto the UK's statute books, even after Biden was elected and after it was this week handed a crushing defeat in the House of Lords, the UK's upper chamber.

A readout from Downing Street did not mention the Good Friday Agreement and said that the Prime Minister and President-elect discussed issues including working together through NATO, and climate change.

A Downing Street spokesperson said: "In a call this afternoon the Prime Minister warmly congratulated Joe Biden on his election as President of the United States.

"The Prime Minister also conveyed his congratulations to Vice President-elect Kamala Harris on her historic achievement," said Downing Street in a statement emailed to Business Insider.