New Delhi, May 12 -- British Prime Minister Keir Starmer pledged Monday to prove the "doubters" in his own party and among the electorate wrong as he struggled to fight off growing demands to step down after devastating local election results for his Labour Party.

Starmer said he would "face up to the big challenges" and restore hope to the country, in part by forging closer ties with the European Union, six years after the U.K.'s acrimonious departure from the bloc.

"I know I have my doubters and I know I need to prove them wrong, and I will," Starmer said during a speech in London intended to kickstart his fightback against detractors.

It did not appear to have the intended effect. In the hours after the speech a steady stream of Lab...