Detectives believe an armed gang has staged its latest hold-up in a string of attacks on a Bradford supermarkets.

Staff were threatened at gunpoint as the masked raiders grabbed cash from the Co-op Late Shop in Heights Lane, Daisy Hill, as the store was preparing to close on Thursday.

At 10.45pm, two African-Caribbean men wearing balaclava masks burst in, one brandishing a handgun.

Detective Inspector Tony Craven, of Bradford North CID said: "They threatened the three members of staff with the gun and pushed them around before taking an amount of cash from the till."

He said the workers were left traumatised but suffered no injuries.

Det Insp Craven added: "This appears to be the latest in a series of similar incidents.

"We are investigating links between this robbery and a number of offences within the division, outside of it and possibly outside the force area."

The raid came as Co-op bosses - who have now suffered eight armed raids across the county within two months - joined with other outlets to offer a £5,000 reward for evidence helping to cage the gang.

The region's Major Crime Unit has been called in to investigate robberies at Co-ops and other stores across Bradford, Leeds, Huddersfield and Harrogate.

In Bradford, three Co-ops, including Beacon Road, Buttershaw, and Broadstone Way, Holme Wood, have already been robbed.

Det Insp Craven said that, unlike in earlier offences, the robbers at Daisy Hill were seen escaping in a car - a blue Vauxhall Astra.

He said: "We would like to hear from anyone who had been in the shop, who lives in the area or was close by before or afterwards who may have seen the car or anyone acting suspiciously."

Detective Chief Inspector Allan Doherty, head of the Major Crime Unit in Leeds, said officers from the force's Operation Support Unit had been stepping up patrols in strategic areas.

He added that officers were working closely with stores on how to up their security and advised workers and customers not to confront the robbers.

Last month Yorkshire Co-operative's chief executive David Marks wrote to West Yorkshire's Chief Constable demanding more action to protect his staff.