LONDON - British police are warning parents about a social media "game" which has reportedly been linked to teenage deaths in Russia, media reports say.

The blue whale challenge is said to involve people being set a series of tasks over 50 days - ending in them taking their own lives, the BBC reported on April 26.

However, there is no evidence that the game is real.

In the game, players are given tasks by an anonymous "master".

The tasks reportedly escalate from straightforward demands, such as watching a scary film, to those increasingly dangerous ones such as self-harming.

Police in Hertfordshire have advised parents "to be vigilant and monitor children's internet usage".

Hertfordshire Constabulary's deputy head David Wright told BBC: "There's no evidence to say anything untoward is going on with the blue whale challenge in our school, but we feel it's best to keep parents and carers informed."

According to The Sun, no deaths in Britain have been linked to the game.

Unconfirmed Russian media reports have linked the deaths of two teenage girls to the challenge, the BBC said.

The name of the game seems to be a reference to the way some blue whales beach themselves on purpose and die.

Bulgaria's Centre for Safe Internet told the Balkan Insight that the game is probably a rumour that has been spread online.

It added that there is no concrete evidence that the challenge exists.