Young men are being targeted in a blackmail scam which sees a woman attempt to lure them into carrying out explicit acts on Skype before demanding money, police have warned.

Victims are told to pay hundreds of pounds or footage of them will be posted to their family and friends, detectives said.

Hertfordshire Police, which raised the alarm after receiving 20 reports so far this year, said it believes the con is being carried out around Britain.

The force said: "The men, whose ages range between 17 and 36, are contacted by a 'young attractive woman' via social media and encouraged to have conversations via the online video chat service, Skype.

"The woman encourages the victim to perform a sexual act for her to view.

"The victim is contacted shortly after by the perpetrator who claims they have videoed the event and demands money. The victim is told that the video will be posted to their friends and family via social media if they do not pay the money."

Men are approached on various sites but "predominantly" through friend requests on Facebook.

In some cases money has been transferred, including sums in the region of £500, police said.

Detective Inspector John Hazeldine said: "This is a scam which we believe is taking place across the country, and not confined to Hertfordshire.

"However, it is important that young men are made aware that this is taking place so they do not fall victim."