RIYADH, Nov 26 (Reuters) - More cases of a deadly strain of bird flu have been found at a poultry farm in Saudi Arabia just weeks before the Muslims flock to Mecca for the annual haj pilgrimage, the Ministry of Agriculture said on Monday.

A statement published on the official Saudi Press Agency said all birds at the farm at al-Kharj, 150 km (94 miles) south of Riyadh, were culled on Thursday after the H5N1 strain was found there. It gave no more details.

Saudi authorities killed 50,000 birds in al-Kharj earlier this month after 1,500 birds died of unspecified causes and inspection teams have since then culled thousands more at markets around the capital of around 4 million people.

The discovery comes just a few weeks before nearly 2 million faithful arrive for the haj pilgrimage season in Mecca.

The virus has caused more than 200 deaths in humans globally since 2003, according to World Health Organisation data.

Although most people who have caught bird flu have had direct or indirect contact with infected fowl, experts fear the constantly mutating virus could change into a form easily transmitted from person to person.

The Saudi government says it has large stocks of Tamiflu anti-flu tablets in case the virus spreads to humans.

In March, Saudi Arabia said the deadly H5N1 strain of bird flu had been discovered in peacocks, turkeys, ostriches and parrots at a house in the east of the kingdom and that an unspecified number of birds in the area had been culled. (Reporting by Andrew Hammond; editing by Dominic Evans)