British authorities battling the spread of bird flu virus say they are destroying poultry at four more sites in eastern England as a precautionary effort to deal with the outbreak.

Authorities say poultry has been identified as having close contact with people who visited a free-range turkey farm northeast of London, where the virus was discovered earlier this week.

Authorities emphasized Wednesday that the new slaughter measures are precautionary.

England's chief veterinary officer confirmed Tuesday that the H5N1 strain was detected on the free-range farm.  He said the virus is related to the type found in the Czech Republic and in Germany months ago.

A February outbreak of the virus in the same region led to the slaughter of 160,000 turkeys.

The World Health Organization (WHO) says more than 200 people have died of bird flu worldwide since the outbreak of the disease in 2003. Most of the deaths have been recorded in Asia.

Some information for this report was provided by AFP and Reuters.