The European Union congratulated incoming British Prime Minister Boris Johnson on Tuesday but warned of “challenging times ahead” and ruled out heeding his election pledge to renegotiate Brexit, reports Reuters.

The European Commission said it was keen to work with Johnson.

“We look forward to working constructively with PM Johnson when he takes office, to facilitate the ratification of the withdrawal agreement and achieve an orderly Brexit,” said the EU negotiator, Michel Barnier.

“We are ready also to rework the agreed declaration on a new partnership,” he added, referring to a political declaration on wished-for future relations that accompanies the legally binding withdrawal agreement.