The victim, aged in her twenties, had been walking on the footpath that passes under the viaduct between Domestic Road and Cross Ingram Road between 9.15am and 9.20am yesterday.
She was grabbed from behind by a male who dragged her to a nearby grassed area. He was disturbed by a passer-by and ran off.
The suspect was described as wearing a black jacket with a fur-trimmed hood, a black beanie hat, and a black face covering over his mouth.
Detectives from West Yorkshire Police Homicide and Major Enquiry Team are carrying out extensive enquiries to identify the suspect and are keen to hear from anyone who was in the area and witnessed the incident.
Senior Investigating Officer, Detective Chief Inspector Tony Nicholson said: “The victim has been left traumatised by this attack and we have specially-trained officers supporting her as we continue to carry out enquiries to identify the person responsible.
“We are treating this incident very seriously and would like to hear from anyone who was in the area and witnessed anyone acting suspiciously or saw the suspect running off in the direction of Armley Gyratory.
“We appreciate that an incident of this nature will cause understandable concern in the community and we are liaising closely with our colleagues on the local neighbourhood policing team who are increasing their presence in the area to reassure people.”
Anyone with information is asked to contact the investigation team via 101 quoting Operation Palmerston reference 13220240427 or online via www.westyorkshire.police.uk/101livechat.
Information can be given anonymously to the independent charity Crimestoppers on 0800 555 111.