Elon Musk is “interfering in our politics” and attempting to create division, Keir Starmer has said in a significant toughening of government language about the X owner.

It comes after weeks of posts by Musk on his social media platform about the murder of Henry Nowak, many of which have used far-right themes and talking points.

Starmer was due to meet Nowak’s family at Downing Street later on Thursday to discuss a response to the actions of Hampshire police, who arrested the teenage student as he lay dying from stabs wounds after a false accusation of racist abuse by the killer.

Starmer, speaking in Yorkshire, where he was due to meet mayors from English regions, said Britain needed to “assert who we are” as “reasonable, tolerant people”.

He praised the Labour MP Jess Asato, who is taking legal action against Musk’s xAI company after saying its Grok tool helped a user produce fake sexualised pictures of her, part of a wave of images that flooded X earlier this year.

“Jess Asato is absolutely right in the action she is taking. Disgusting images were created, in her particular case by Grok,” said Starmer, who has warned Musk’s company it would face drastic regulatory action if it did not stop the flow of sexualised images, some of which featured children.

Starmer said: “I am really pleased that we took Grok on a few months ago, because that is the fight we should be in, taking on some of these platforms providers [and] some of these disgusting images, really disgusting. We won that.

“But Jess is right, she is a parliamentarian. I am 100% behind the action that she has taken.

“We also need to assert who we are as a country because Musk again has been interfering in our politics in the last few days, trying to whip up division. That is not who we are in Britain.

“In Britain we are reasonable, tolerant people. When we have a terrible case like Henry’s case, Henry Nowak, we react calmly as his family has done.

“When it comes to disgusting images on Grok, we take Grok on and fight because that’s who we are as a country.”

Musk is a regular poster of ethnonationalist content, and is a strong supporter of Restore Britain, the far right party set up by Rupert Lowe, the former Reform UK leader.

Speaking later, Starmer’s spokesperson did not specify any particular posts from Musk that raised concern. It is understood to be based more on the overall tone of his content, particularly over the Nowak case.

In recent weeks Musk has repeatedly argued that the case of Nowak, who was arrested by police as he lay dying from stabs wounds inflicted by Vickrum Digwa, shows the UK is biased against white people.

Numerous posts on X by other users have falsely identified two Hampshire officers, one of whom has left the force, as being involved in Nowak’s arrest, with the former officer being forced to go into hiding.

Starmer’s spokesperson said this type of misinformation was a matter for Ofcom, the media regulator. She said neither the prime minister nor the government had plans to stop posting on X.

Starmer was due to meet Nowak’s family for what was described as a private meeting. It comes after Kemi Badenoch, the Conservative leader, met Nowak’s mother, father and stepmother.

Badenoch wrote: “Henry’s family do not want anger to tear communities apart. They are a family who have friends across faith and race, and so did Henry. His family want his memory to help bring our society together.”

The police watchdog is examining the conduct of the officers who handcuffed Nowak, 18, after he had been fatally stabbed by 23-year-old Digwa. They had gone to the scene in Southampton after Digwa falsely claimed he had been racially abused and attacked by Nowak.

Eleven police officers and one police dog were injured on Tuesday night after crowds including far-right agitators attacked officers in Southampton in what was billed as a protest about Nowak’s death and his treatment by police.

Meanwhile, in a claim submitted to the high court in London, Asato said xAI – now a subsidiary of SpaceX, which also owns X – breached laws connected to data protection and the misuse of private information by letting users of the site prompt Grok to create such images.

Asato has said that as well as creating images of her in a bikini, Grok produced a video “showing her being chloroformed and prepared for a sexual assault”.