KARACHI, April 9 (Reuters) - Pakistan reported new bird flu cases on Monday in commercial poultry farms in the southern province of Sindh and in North West Frontier Province, a government official said.

"Two to three days back we found traces of H5N1 virus in small poultry farms in Sindh and NWFP," Mohammad Afzal, Commissioner for Livestock at the Ministry of Food and Agriculture, told Reuters.

"We have culled all the birds at these farms and disinfected the area."

He said some 300 to 350 birds had been culled at one farm but did not say how many H5N1 cases of bird flu had been discovered.

Since late last year, outbreaks of avian flu have swept from Asia to Britain, as well as touching Egypt and Nigeria.

Several outbreaks have been detected in chickens in small poultry farms this year in Pakistan and birds have been culled.

Authorities temporarily shut Islamabad Zoo in February after four peacocks and a goose died of the H5N1 strain. Pakistan has had no human cases of the virus.

Afzal asid quarantine and vaccination measures were also being used in and around the affected farms.

Pakistan first detected the H5N1 strain of the virus in February 2006 in North West Frontier Province and ordered about 40,000 birds culled.

Since 2003, the H5N1 virus has killed at least 170 people around the globe and experts fear it could mutate into a form that could jump easily between people and cause a pandemic.