A series of cable thefts have been carried out by a sophisticated team that may be posing as rail workers, police say.
British Transport Police, which is investigating a number of thefts on rail lines in Gloucestershire and Worcestershire, said the thieves have targeted signalling cable, causing disruption to the network as well as expensive replacement costs.
The thieves have also left cabling in a dangerous condition, which police said could cause injury to others.
"They clearly have some specialised knowledge and it would take them time to carry out the thefts," Detective Chief Inspector John Pyke said.
"That makes us think that they may be posing as rail engineers so as not to arouse suspicion."
He added that police believe the group is responsible for at least four incidents so far, including at Chipping Campden on 15 November, at Eckington on 3 December, at Honeybourne on 8 December and at Evesham on 14 December.
"They choose very rural locations and must be using one or more vehicles to take the cable away," Mr Pyke said.
"We need members of the public who live near lines in those areas to report any activity they see that might be connected with this type of crime - whether the people involved are wearing railway high visibility jackets or not.
"We can quickly check whether they are bona fide engineers. Abandoned vehicles near to rail lines are also of interest to us."
Anyone with information is asked to contact British Transport Police on 0800 405040 quoting reference B8 of 19 December, alternatively they can contact Crimestoppers anonymously on 0800 555 111.