Britain’s new top diplomat, Boris Johnson, swept into office Thursday on a cloud of acrimony, amid worldwide disbelief that the irreverent campaigner for a British break from the European Union will now be his nation’s main voice abroad.

From composing a dirty limerick about the Turkish president and a goat to comparing the E.U. to Hitler and calling Hillary Clinton a “sadistic nurse,” the mop-haired Johnson spared few world leaders in his previous career as the devil-may-care mayor of London. This time, he was on the receiving end: France’s foreign minister declared that the “leave” campaigner had “lied a lot,” and Germany’s top diplomat called him “irresponsible.”

The unusually sharp rhetoric from Johnson’s new peers reflected the degree to which he has alienated Britain’s global partners and the challenges he faces as he takes part in his nation’s divorce from the E.U. From Washington to Paris and Berlin to Ankara, leaders uttered bitter cries of surprise at the appointment of a man who has reveled in dishing offense, not making friends. Critics said Britain appears to be taking further steps to disengage from the world.

“I have no worries about Boris Johnson, but you know well what his style is,” French Foreign Minister Jean-Marc Ayrault told France’s Europe 1 radio on Thursday. “He lied a lot during the campaign.”

Ayrault was referring to a range of later-discredited claims by the anti-E.U. side before last month’s referendum on a British exit from the European Union, including the amount of money Britain pays to the E.U.

The criticism from the usually buttoned-down Ayrault is almost without precedent in the discreet world of European diplomacy, where top leaders typically attack one another’s policies, not their characters.

It foretells the reception that Johnson is likely to receive during the coming years of fraught negotiations with the 27 other E.U. foreign ministers, almost all of whom personally blame him for the chaos unleashed by the British decision to leave the bloc. The ministers will meet in Brussels on Monday in Johnson’s first test as foreign secretary. 

“Sorry world,” read a cardboard sign that one British wag tied to the gate of Johnson’s London residence, captured on camera Wednesday night by Sky News.

The Sky News journalist noted to Johnson that he would have a long list of people to apologize to, including President Obama. In April, Johnson criticized Obama as a “part-Kenyan” who harbored anti-British attitudes because his father’s nation was once part of the British Empire. 

Barely stifling a smirk, Johnson said that “the United States of America will be in the front of the queue.”

Johnson will have to contend with France and Germany — the E.U.’s most powerful nations — and potential roadblocks to any advantageous deal for Britain as it navigates its split from the bloc. German and French politicians may have little tolerance for a man who during the referendum campaign in Britain compared E.U. efforts to unify Europe with Napoleon and Hitler.

“Boris Johnson doesn’t do good personal relationships with other politicians,” said Simon Tilford, deputy director of the London-based Center for European Reform.

Johnson’s German counterpart, Frank-Walter Steinmeier, also appears to hold a dim view of the newly minted British diplomat.

Hours before Johnson’s appointment was made public Wednesday, Steinmeier lashed out at him without using his name, criticizing “irresponsible politicians” who lured Britain toward a “Brexit” and then “didn’t take responsibility and instead played cricket.”

Johnson disappeared from public view in the days after the referendum and instead played cricket at a friend’s country estate.

In a short session with reporters outside the British Foreign Office on Thursday, Johnson shrugged off in his typically colorful fashion the European expressions of horror at his appointment.

“After a vote like [the referendum], it is inevitable that there is going to be a certain amount of plaster coming off the ceilings in the chancelleries of Europe,” he said. Asked about the French foreign minister’s assertion that Johnson had lied during the referendum campaign, he suggested that Ayrault had taken a very different tone in private communications.

Johnson said that he was determined to ensure that Britain remains “a great global player” and that he and U.S. Secretary of State John F. Kerry, speaking by telephone Thursday, had agreed on the need to maintain Britain’s leading role in world affairs. The two will meet Monday in Brussels.

Johnson has taken a softer line toward Russian actions in Ukraine than his predecessor, blaming the E.U. in part for the crisis there. And he has advocated working with Syrian President Bashar al-Assad to defeat the Islamic State militant group, an idea that is anathema to many in Washington and Europe.

Johnson’s fellow Conservatives generally stood firm behind the appointment, having resolved to end the internecine warfare that has nearly torn the party apart in recent months.

But the opposition Labour Party reacted with dismay. Angela Eagle, who is challenging party leader Jeremy Corbyn for his job, was making a campaign speech when a member of the audience shouted out the news. “They’ve just made him foreign secretary?” she asked, bewildered, before whirling her back toward the crowd in shock.

Johnson’s day-to-day involvement in Brexit negotiations has yet to be defined, with two other Euro-skeptic leaders taking prominent roles in Prime Minister Theresa May’s new government. David Davis, another “leave” campaigner, was given the new role of “secretary of state for exiting the E.U.” In Europe’s complex decision-making system, foreign ministers typically focus on E.U. relations with the rest of the world, not issues within the union’s borders. But Britain is now a special case.

Still, foreign ministers are often to be found heading faraway missions to places such as Papua New Guinea — which Johnson once suggested boasted orgies of cannibalism and chief-killing — or Washington. That may have been one of May’s strategies in appointing Johnson to the job, sidelining a critic who otherwise would have taken aim at her from his column in the Daily Telegraph.

One of the biggest disruptions of Johnson’s appointment may be to U.S.-British relations — an irony because he was born in New York, and public documents released in May showed that he was still a dual U.S.-British citizen. Because the United States taxes its citizens on earnings across the world, Johnson owed U.S. taxes on the 2009 sale of his London home, a bill he paid only last year, according to British news media.

“This is someone who at times has appeared to discount the relationship,” said Julianne Smith, a national security analyst at the Washington-based Center for a New American Security, who has served in the Obama administration.

“He’s a very prickly personality and doesn’t appear to be someone who has spent much time thinking about foreign policy,” she said, joking that the general reaction in Washington to the appointment was “shock and awe.”

Turkey is another nation where Johnson will have to lobby for couples counseling. In May, he penned a naughty limerick suggesting that Turkish President Recep Tayyip Erdogan had “sowed his wild oats with the help of a goat, but he didn’t even stop to thankera.”

“May God help him and reform him,” Turkish Prime Minister Binali Yildirim told the BBC on Wednesday, before Johnson’s appointment was announced. “And I hope that he won’t make any more mistakes and try to make it up with the Turks.”

Witte reported from London. Ylan Mui in Washington contributed to this report.