LONDON, Nov 15 (Reuters) - A deadly bird flu virus may have spread to another site in Britain, with suspicious deaths at a turkey farm in Suffolk, the farm ministry said on Thursday.

"During preparations for culling at one of the premises which is located in the protection zone, a notifiable disease could not be ruled out," a spokeswoman for the Department for Environment, Food and Rural Affairs (Defra) said.

The deadly H5N1 bird flu strain was confirmed at a farm in eastern England earlier this week. Suspicious deaths of turkeys at a nearby farm led to fears that virus may have spread, she said.

"All the poultry on the Suffolk premises are being culled under the slaughter-on-suspicion policy. At this stage we cannot confirm whether or not the disease is present," she added, noting samples had been taken and results were awaited.

Redgrave Poultry said the disease was originally confirmed at the Redgrave Park farm near Diss, Norfolk. The company said on Thursday the second site was Grove Farm in Botesdale.

Grove Farm shares the same workforce as Redgrave Park.

Defra said 5,500 free-range turkeys would be culled at the second farm.

"Defra vets found about 0.5 percent loss in the flock at Grove farm yesterday. It is worth noting that a normal aspect of production is the loss of a small proportion of birds," Redgrave Poultry said in a statement.

Defra had announced on Wednesday that poultry would be culled at four sites which had "dangerous contacts" with the infected farm as a precautionary measure. Redgrave said these included Grove Farm.

The virulent H5N1 strain has killed more than 200 people worldwide since 2003 and millions of birds either have died from it or been killed to prevent its spread.

Britain"e;s farm ministry has imposed a 3-km (2-mile) protection zone, 10-km (4-mile) surveillance zone and a wider restricted zone. In these areas, poultry must be isolated from wild birds and there are movement restrictions.

Britain had an outbreak of the H5N1 virus strain in February at a turkey farm in Suffolk, eastern England. (Reporting by Nigel Hunt; Editing by Michael Roddy)