British Prime Minister Keir Starmer defended his work as Britain's top prosecutor on Monday, refusing to mention US billionaire Elon Musk by name but addressing his criticism that, long before he became leader, he had failed to prosecute gangs who sexually abused girls.

Musk, a close ally of US President-elect Donald Trump, has spent days posting messages on his social media site X accusing Starmer of what he said was a failure to prosecute gangs of men, mostly of a South Asian background, who raped young girls when he was director of public prosecutions (DPP) between 2008 and 2013.

Starmer declined to address some of Musk's other messages on X - including a poll asking whether the United States should liberate the UK from its "tyrannical government" - but strongly defended his record as DPP, saying he had overcome resistance to tackling the allegations by reopening cases.

"When I was chief prosecutor for five years, I tackled that head-on ... and that's why I reopened cases that had been closed and supposedly finished. I brought the first major prosecution of an Asian grooming gang ... I changed the whole prosecution approach," he told a press conference, visibly angry.

"Those that are spreading lies and misinformation as far and as wide as possible are not interested in victims, they are interested in themselves."

Starmer has refrained from commenting on Musk's increasingly critical comments of his tenure, but his impatience was clear when he tackled the allegations over cases involving gangs who systematically groomed and raped girls over a period of years, some of which coincided with his time as DPP.

A 2014 inquiry found at least 1,400 children were subjected to sexual exploitation in Rotherham, northern England, between 1997 and 2013. (Reuters)