Pupils as young as 11 are being encouraged to join in school fights in posts on TikTok and Snapchat, prompting police to urge children not to get involved.

The Metropolitan police have asked social media platforms to ban accounts promoting “school wars”, while headteachers have warned parents about the posts.

One of the posts advertised a “north London war” between pupils from year seven to 11, pitting four named schools on a “red side” against four on a “blue side”. Another promoted a “Hackney war” using images of weapons to bring, including knives, compasses and fireworks.

Other posts have suggested a points systems based on the harm done to opponents, urging participants to “be violent”.

Commander Neerav Patel, from the Met, said the force was aware of the posts and was in contact with several London boroughs to offer reassurance.

He said: “We continue to closely monitor online spaces and have worked with platforms to request a dozen social media accounts to be disabled where threats or violence were planned or encouraged.”

In a message to pupils, he said: “I would like to remind young people of the serious consequences of getting involved in matters like this. An arrest, charge and conviction for violence and carrying weapons could mean imprisonment, with a significant long-term impact on future opportunities.”

A previous attempt to organise a school fight in Hackney prompted police to issue a dispersal order.

Several London schools have sent letters to parents about the posts. A letter from Fortismere school, in Haringey, north London, said: “We are writing to alert you to recent social media activity circulating across various parts of London that encourages young people to take part in so called ‘tagging’ or ‘schools wars’ –style games.

“Thank you to parents who have approached us with concerns they have had when checking their children’s phones.”

Graveney school in Tooting, south-east London, told parents: “We will ensure that our usual security measures are deployed effectively, including using our ability to search students if necessary.”

But pupils are sceptical about the veracity of the posts, which some believe to be spoofs, according to the Metro, which first reported on the issue. It quotes one year 10 pupil saying: “People are just trying to fearmonger parents … Any teenager with common sense would not meet somewhere where the police have been told about and bring a weapon.”

The health secretary, Wes Streeting, said he had flagged the issue to colleagues. MailOnline reported that he wrote underneath one of the posts: “I’ve raised this at highest levels in government. Hope parents are clear with their children that we’ll come down on this sort of behaviour like a ton of bricks.”