A petrol station and nearby convenience store in Sheffield were held up on the same night - in incidents which police believe may be linked.
In the first raid at 8.05pm on Sunday a man posing as a customer walked into Sainsbury’s petrol station at Crystal Peaks and when the till was opened the culprit pushed the assistant and attempted to grab the money inside.
But police said his efforts failed and he left empty-handed.
He was white, around 18 or 19 years old, 5ft 4ins tall, of a large build and wearing a grey tracksuit and blue padded body warmer.
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One hour later Beighton Convenience Store was robbed by a man armed with a knife.
He threatened a member of staff demanded cash, which was handed over.
The robber was white and wearing a grey long-sleeved top under a dark padded body warmer.
A South Yorkshire Police spokeswoman said: “Police believe the two incidents may be linked.”
Earlier this month a masked robber raided the High Street service station in Beighton after threatening a worker with a gun.
The robber, believed to be aged between 16 and 18, took cigarettes and cash in the raid.
Police said none of the members of staff involved were injured in any of the incidents.
Store manager Marilyn Jones, of High Street service station said the gunman said to her employee ‘Give me the money or I will blow your brains out’.
Mrs Jones said the woman handed over more than £400 in cash, and around £80 worth of cigarettes.
Anyone with information should call police or Crimestoppers on 0800 555111.