Wires have been strung between trees at least twice in a Brighton wood.
Sussex Police said: “Walkers, cyclists and others using tracks through Coldean Woods in Brighton are being warned to look out for wires being strung between trees to create danger.
“Two such incidents have been reported to police in as many days and there are fears that someone may be seriously injured if they fail to spot the obstacles.
“Officers have been working with Brighton and Hove City Coucil rangers to remove the wires and extra foot patrols are being mounted in the area.”
Sergeant Alison Penny, of the East Brighton Neighbourhood Policing Team, said: “These wires appear to have been deliberately placed across paths.
“There is a real risk that someone could run into them and suffer serious injury as a result.
“It is an extremely foolhardy thing to do and those responsible can expect to be dealt with robustly. Extra patrols are on the lookout for offenders.
“Meanwhile, I would urge people using the woods to take care and also to report any suspicious behaviour without delay.”
Anyone with information is asked to phone Sussex Police on 101, email firstname.lastname@example.org or call the independent charity Crimestoppers anonymously on 0800 555111.