This took the global total to 113 deaths out of 204 cases since 2003, the United Nations agency said.

Egyptian officials had previously announced all 12 cases, including the fourth fatality, an 18-year-old girl from a province north of Cairo who died a week ago.

In a statement, the WHO said one of its collaborating laboratories in Britain had now "fully validated" the test results obtained in Egypt.

The highly pathogenic H5N1 virus was detected in birds in Egypt in February and the first human infection was reported in mid-March. All four victims have been women, who are often responsible for slaughtering and cooking domestic poultry.

"Of the 12 cases in Egypt, four patients have died and one remains hospitalised in stable condition," the WHO said.

The remaining seven patients had fully recovered, it added.

On Thursday, the WHO said a man in neighbouring Sudan suspected to have bird flu had now tested negative.