Emotion reading technology could soon be used by police after a Russian firm created a tool that can identify people in a crowd and tell if they are angry, stressed or nervous.

The software, created by NTechLab, can monitor citizens for suspicious behaviour by tracking identity, age, gender and current emotional state. It could be used to pre-emptively stop criminals and potential terrorists.

"The recognition gives a new level of security in the street because in a couple of seconds you can identify terrorists or criminals or killers," said Alexander Kabakov, NTechLab chief executive.

The emotion recognition tool is a new part of NTechLab's facial recognition software, which made the headlines last year when it was used to power the FindFace app that can track down anyone on Russian social network VKontakte from a photo.

The identification app claims to have reconnected long-lost friends and family members, as well as helped police solve two cold cases and identify criminals.