Juncker called the existing deal "the best and only agreement possible." Juncker and Johnson had their first phone conversation late Thursday since Johnson took over from Theresa May as Britain's leader.
Johnson has insisted that the current agreement to leave the EU and arrangements regarding the Irish border were not good enough and had to be renegotiated. An EU official with knowledge of the exchange said that despite Juncker's refusal to reopen the legal 585-page legal agreement, Juncker said he "remains at the disposal of the United Kingdom to add language" to a political text on future relations and "to analyze any ideas put forward by the United Kingdom, providing they are compatible with the withdrawal agreement."
The official spoke on condition of anonymity because of the confidentiality of the phone call.
European Commission President Jean-Claude Juncker and new British Prime Minister Boris Johnson will have a phone call later Thursday to discuss the prospects of reaching an orderly departure of Britain from the bloc.
EU Commission chief spokesperson Mina Andreeva said the phone call is planned for 5.45 p.m. Brussels time (1645GMT).
Johnson has insisted that he wants to renegotiate the withdrawal deal both sides agreed on under Prime Minister Theresa May. EU leaders have firmly refused to consider the option and said they only want to discuss changing an additional political text outlining future arrangements.
Johnson has said that is not good enough for him, and has threatened to walk out on the deal and leave the EU on Oct. 31 in a so-called cliff edge scenario.
Economists have said a no-deal exit would be chaotic, and expensive for Europe but even more so for the United Kingdom.
British Prime Minister Boris Johnson has called on the European Union to "rethink" its refusal to renegotiate the Brexit deal.
Addressing the House of Commons for the first time since becoming prime minister, Johnson said Britain would throw himself into efforts to make sure Britain leaves the EU on time on Oct. 31.
He insisted that Thursday is the first day of a new approach.
Rejecting "skeptics and doubters," he said he is intent upon re-energizing "our great United Kingdom and making this country the greatest place on earth."
"And when I say the greatest place on earth, I'm conscious that some may accuse me of hyperbole, but it's useful to imagine the trajectory on which we could now be embarked."
Britain's main opposition Labour Party has rejected calls for an immediate vote of no-confidence in the new government of Prime Minister Boris Johnson.
Liberal Democrat leader Jo Swinson urged Labour to back an attempt to bring down the government on Johnson's first full day in office. She says Johnson, who was elected to replace Theresa May by two-thirds of the Conservative Party's 160,000 members, "holds no mandate from the public or Parliament."
But Labour, whose support would be needed for a vote to succeed, rejected the idea, saying "a no confidence vote now will only strengthen Boris Johnson's hand."
For a no-confidence vote to succeed, a handful of Conservative lawmakers would have to vote against their own government — something they are unlikely to do on its very first day.
Thursday is Parliament's last sitting day until September.
Boris Johnson is convening his first Cabinet meeting as Britain's prime minister, pledging to break the impasse on issues that flummoxed predecessor Theresa May.
Johnson has less than 100 days to make good on his promise to deliver Brexit by Oct. 31 after what he called "three years of unfounded self-doubt."
The new Cabinet arrived early at Johnson's Downing Street office — a collection of fresh faces after Johnson culled senior members of May's team. The new line-up includes Foreign Secretary Dominic Raab, Treasury chief Sajid Javid and House of Commons leader Jacob Rees-Mogg.
In his first speech as prime minister, Johnson offered a plethora of promises, from more police on the streets to ending a ban on genetically modified crops to faster internet access.
Follow AP's full coverage of Brexit and the Conservative Party leadership race at: https://www.apnews.com/Brexit