MASKED robbers armed with knives have threatened staff in at least 15 small shops in County Durham, The Northern Echo can reveal.

All the attacks have involved kitchen knives and the robbers have hidden their identities with scarves and balaclavas.

Police investigating the attacks, which have left shop staff traumatised, say they may be linked.

The robbers are thought to have got away with several thousands of pounds.

In the Darlington area there have been 11 armed robberies and attempted robberies since January 14. But, it started in October with robberies in Newton Aycliffe and Durham City.

Detective Sergeant Dave Storey, of Darlington police, said: "There are other robberies that have occurred in Ferryhill and Newton Aycliffe and we know there are similar crimes that have happened in Willington and Consett.

"In the majority of them, those responsible had their faces concealed."

Four men have been arrested in connection with some of the robberies in Darlington and Newton Aycliffe, the latest of them appearing in court on Saturday.

But police believe more people are involved. They have previously said at least two gangs are thought to be operating and yesterday appealed from the public to come forward with more information.

Police have reminded shopkeepers to ensure their closed-circuit television systems are in working order.

Anyone who can help is asked to call police on 0845 60 60 365, or Crimestoppers on 0800 555 111.