Wes Streeting has called for Keir Starmer to take urgent action against X and other online platforms that have helped whip up social tensions, suggesting they should be forced to contribute to rebuilding costs after the riots in Belfast.

The intervention by the former health secretary, who is seen as a likely challenger to Keir Starmer in any leadership contest, comes after Downing Street said any response would be left to Ofcom, the media regulator, meaning no action is likely for at least two months.

Condemning what he termed “the forces of darkness online and offline”, Streeting said this was an insufficient response to a mass of posts on X – including from the platform’s trillionaire owner, Elon Musk – calling for an angry response to a knife attack in Belfast.

It follows a similar pattern of incitement before disorder in Southampton in response to the case of Henry Nowak, who was handcuffed by police as he lay dying after his murderer falsely accused the teenage student of racist abuse.

As well as calls from far-right agitators, such as Tommy Robinson, for people to protest, X carried large numbers of posts incorrectly naming two people as being among the Hampshire police officers involved in Nowak’s arrest, with some showing addresses and messages such as: “Wanted: dead or alive.”

In a statement to the Guardian, Streeting said: “We’re long past the time for threats. We have to act. Incitement to violence is a crime in the offline world so it must be prosecuted as a crime in the online world.

“If platforms are knowingly promoting this dangerous content, bosses should face criminal action and the companies should be made to pay the costs of cleaning up and rebuilding Belfast, along with the thugs on the ground.

“We’ve been far too timid in the face of broligarchs attempting to reshape our society and inspire hatred – we should be standing up to the forces of darkness online and offline, and we still can.”

The Online Safety Act requires social media companies to remove any posts that break the law, for example by inciting violence, with Ofcom enforcing this. X has agreed with the media watchdog that it will send a quarterly report setting out its compliance on this, but the first of these is not due for at least two months.

Ministers also plan to amend the Online Safety Act to require social media firms to act more quickly to remove inflammatory content during riots or other crises. However, this has to be laid before parliament for 40 days, so will not take effect until mid-July at the earliest.

In contrast, after X was flooded with sexualised images of women and children generated by its Grok AI tool, Starmer threatened the platform with being blocked in the UK if it did not take urgent action to tackle the problem, prompting X to stop the tool being used via the Grok account and in Grok in X.

Asked why similar action was not being taken over posts inciting violence in Belfast or Southampton, Downing Street has pointed to existing action being taken by Ofcom for breaches of the Online Safety Act, with some platforms having been fined.

A No 10 spokesperson said: “We condemn anyone who has attempted to stoke division or incite violence, and those breaking the law should face the consequences, whether it’s offline or online.

“We will not tolerate platforms being used to spread harm, abuse or division. Platforms have clear responsibilities in law to remove any illegal content, and Ofcom have our full backing in using their enforcement powers to hold them to account.”