Women are being warned to avoid walking alone in the dark after three similar sex attacks took place in the same county in six months.
The three incidents happened within Gloucestershire and while they are not formally being linked police said they are investigating similarities in the crimes.
In two cases the offender wore a balaclava during the attacks on women aged 16, 18 and 20.
A team of detectives has been assembled to investigate the sexual offences which took place in Cheltenham, Innsworth and Gloucester between November last year and earlier this month.
Two men from the Gloucester area have been arrested and since released on police bail, Gloucestershire police said.
Detective Sergeant Angela Middlewood said: "These are three crimes in which young women were targeted by strangers in public places, which, fortunately, is relatively rare in Gloucestershire.
"We are investigating all three crimes together because of similarities between them, but we have not formally established a link at this time and are not sure the same offender is responsible, although it's not something we can rule out.
The first attack took place on 30 November 2011 at around 8.25pm. An 18-year-old woman was grabbed by a man and sexually assaulted as she walked through Welch Road playing fields, in the Hester's Way area of Cheltenham.
On 19 January this year at around 6.45pm a 16-year-old girl was walking across the footbridge from Penrose Road to Evergreen Walk, which crosses the A40, at Innsworth, when she was approached by a man.
The man threatened, assaulted and indecently assaulted the girl, and stole her mobile phone.
The most recent attack took place on 2 May, at around 10.30pm, when a 20-year-old woman was attacked as she walked along a grassed area behind the Clock Tower, near West Lodge Drive, in the Coney Hill area of Gloucester.