DETECTIVES investigating a supermarket robbery are studying possible links to a spate of raids.

Officers last night said they could not rule out the possibility that an attack at Somerfield, in Yarm, near Stockton, yesterday, was connected to five others in recent months.

At least three masked robbers, one of them wielding a hammer, stole several cassettes for a cash machine at the store, in Healaugh Park, shortly after 1.30pm.

The store was immediately closed and cordoned off. Police spent yesterday talking to staff and officers searched the shop for evidence.

The men are believed to have fled the packed store in a getaway car. No one was hurt in the incident.

Police were last night still trying to piece together enough information to issue descriptions of the men and the getaway car.

Staff in nearby shops said they were unaware of the incident until police arrived.

One woman, who asked not to be named, said: "It is a relief, but we do not really take enough money compared to Somerfield."

In the past 18 months, armed gangs have held up security guards at four Tesco stores and a Sainsbury's store. Detectives believe the five incidents are connected to two gangs operating out of Manchester and Liverpool, and are working with officers in the North-West on the cases.

In November 2006, a female security guard was held at gunpoint and forced to hand over money, believed to be five figures, in a raid at Tesco, in Eaglescliffe, near Stockton.

On February 5, last year, a security guard was held up at gunpoint in Sainsbury's, in Bishopton Road West, Stockton.

In February last year, a female security guard was threatened with a sledgehammer by two armed men wearing ski masks as she was filling a cash machine in Tesco Express store, in Norton, near Stockton, at about 7.25am.

In June last year, three men attacked security guards at the Tesco store in Acomb Wood Drive, York, and escaped with a large amount of money.

In July last year, an armed gang held up staff and security guards at the Tesco shop in Parliament Road, Middlesbrough.

A police spokeswoman said last night: "Police are keeping an open mind as to their connection with five other raids."

Anyone with any information is asked to call 01642-326326.