Thames Valley Police is appealing for witnesses following a public order offence in Milton Keynes.
The incident occurred at 2.55pm on Tuesday 17 May outside Marks & Spencer in Milton Keynes Shopping Centre.
The victim, a woman in her twenties, has been followed by a man who she does not know, from outside of Marks & Spencer’s to Midsummer Boulevard towards the job centre.
The offender has then threatened the victim that he would stab and sexually assault her.
The victim asked for help from members of the public and the offender turned and left back towards Centre MK.
The victim was not injured.
The offender is described as a white man, in his thirties, around 5ft 8inches tall with short receding blonde hair. He was wearing a grey t-shirt with a black stripe across the chest with dark tracksuit bottoms, black trainers and carrying a beer can.
Investigating officer PC Fraser Green, based at Milton Keynes police station, said: “I would like to appeal for anyone who witnessed this incident to please come forward.
“If you have any information about this incident, can get in touch by making a report online or calling 101, quoting reference number 43220214034.
“Alternatively, for 100% anonymity, you can also call the independent charity Crimestoppers on 0800 555 111.”