The Labour leader spoke out after the Tory party suspended Lee Anderson over comments he made about the mayor of London.
Sir Keir Starmer has accused the prime minister of harbouring extremists in his party after a senior Tory MP was suspended for “Islamophobic” comments.
The Labour leader said Rishi Sunak’s “weakness” allowed Lee Anderson “to act with impunity” and that he “needs to get a grip and take on the extremists in his party”.
Sir Keir said it was “right” that Mr Anderson lost the whip after what he called an “appalling racist and Islamophobic outburst”.
He added: “But what does it say about the prime minister’s judgement that he made Lee Anderson deputy chairman of his party?
“Whether it is Liz Truss staying silent on Tommy Robinson or Suella Braverman’s extreme rhetoric, Rishi Sunak’s weakness means Tory MPs can act with impunity.
“This isn’t just embarrassing for the Conservative party, it emboldens the worst forces in our politics.”
It came as Mr Sunak released his own statement, criticising those who have threatened and targeted MPs over the ongoing Israel-Hamas war and saying British democracy must not “fall into polarised camps who hate each other”.
Mr Sunak said: “The events of recent weeks are but the latest in an emerging pattern which should not be tolerated.
“Legitimate protests hijacked by extremists to promote and glorify terrorism, elected representatives verbally threatened and physically, violently targeted and antisemitic tropes beamed onto our own parliament building.”
Referring to when the Commons Speaker broke convention in a Gaza ceasefire debate this week out of fears’ for MPs’ safety, Mr Sunak said: “And in parliament this week a very dangerous signal was sent that this sort of intimidation works. It is toxic for our society and our politics and is an affront to the liberties and values we hold dear here in Britain.”
His statement made no mention of Mr Anderson or his comments.