Music-lovers watching their favorite acts at live concerts are increasingly becoming targets for gangs of mobile phone thieves, British police said on Monday.

Detectives warn that they have seen a growing problem of organized criminals at both indoor and outdoor gigs hoping to make off with top-of-the-range phones.

Many victims will also often believe they have lost their phone, perhaps helping to mask the scale of the issue.

We are concerned that organized thieves are targeting concerts to steal phones from genuine fans, said Detective Superintendent Nev Nolan, head of the National Mobile Phone Crime Unit (NMPCU).

A lot of people like to use their mobile phones to film or take photographs of the concert, but will then return the phone to an insecure bag or pocket, where thieves are able to snatch it.

NMPCU said it had made nine arrests at events in London in the last two weeks based on intelligence it had received. Other arrests had been made across the country.

Detectives said they were working with venues to put up posters warning concertgoers to take care of their phones.