Workers at a Bradford supermarket were left terrified after armed robbers fired a gun during a hold-up.

Officers said the incident at the Co-op Food Fair in Thornton Road was the latest in a string of raids on Co-op stores across the city for which they believe the same gang was responsible.

In Bradford at least five Co-op stores have now been targeted, prompting the management to offer a £5,000 reward for information on the culprits. Detectives are investigating links to similar raids on Co-ops in Leeds, Huddersfield and Harrogate.

Yesterday's robbery at the Food Fair was the first time a gun had been fired.

Two men wearing balaclavas burst into the store at 7.55pm yesterday, one of them brandishing a handgun.

Detective Inspector Tony Craven, of Bradford North CID, said the staff had been threatened before the gun was fired and a small amount of cash stolen.

He said: "These men need to need to be caught. This is a serious escalation of violence over the other cases we are investigating."

Witnesses saw the men make off in a white Vauxhall Cavalier, registration H577 BJX, which had been stolen from the Hare and Hounds pub in Toller Lane earlier that day. It was later found abandoned in the Market Street area of Thornton.

Det Insp Craven appealed for anyone who may have seen the car before or after the attack or anyone who witnessed the robbery to contact the police.

Staff at the store confirmed that nobody was physically hurt in the robbery.

The raid came after a Co-op store in Roundhay, Leeds, was held up earlier this week. Other Co-op stores raided include the Co-op in Heights Lane, Daisy Hill, Bradford, and Co-op stores in Allerton Road, Allerton, Beacon Road, Buttershaw and Broadstone Way, Holme Wood.

Anyone with information should contact Bradford North CID (01274) 376059.