LONDON — The bombastic new British prime minister, Boris Johnson, was never likely to offer an olive branch to the European Union that he promises to leave in less than 100 days — without any deal if necessary and whatever the cost.

But any faint hope that Mr. Johnson would adopt a conciliatory stance once installed in Downing Street was dispelled Wednesday night when he axed around half of the cabinet of his predecessor, Theresa May, in a cull that shocked many with its scope and blunt messaging.

In his first statement to Parliament on Thursday, Mr. Johnson doubled down on his hard line, fueling speculation that he was prepared to go to a general election if he is blocked by lawmakers from leaving the European Union without any agreement.

With staunch supporters of Brexit installed in key cabinet positions, Mr. Johnson outlined tough demands on Brexit that Michel Barnier, the European Union’s chief negotiator, immediately described as “unacceptable.”