Four pilgrims have died of swine flu as they take part in this year's annual Mecca pilgrimage, Saudi officials say.

Three of the victims - a woman from Morocco and men from Sudan and India - were in their seventies. The fourth was a 17-year-old girl from Nigeria.

The Health Ministry said none of the four foreign victims had been vaccinated against the H1N1 virus.

The latest figures from the World Health Organization show the virus has so far killed 6,750 people worldwide.

An official statement released by the ministry said all had underlying health problems, including cancer and respiratory illness, AFP news agency reported.

Three of the victims died in Medina and one in Mecca.

Up to three million Muslims from around the world take part in the holy pilgrimage every year, but health officials have expressed fears that it could provide a breeding ground for the virus.

Authorities had tried to prepare for any outbreaks by installing thermal cameras at airports and sea terminals, deploying 15,000 additional health workers and ensuring hundreds of extra beds were available.

Health ministry spokesman Dr Khaled Marghlani told AFP that 16 other people had diagnosed with swine flu and four remain in hospital in "critical condition".

He added 12 others had recovered following treatment.

The Saudi government has said all pilgrims need a certificate of vaccination before they can apply for a visa.

In September, the Egyptian authorities barred hundreds of Muslim pilgrims in Cairo from travelling to Mecca because of fears about the virus.

In July, an Egyptian woman returning from the lesser Umrah pilgrimage became the first person to die of swine flu in the Middle East and Africa.

Performing the Hajj is incumbent upon all Muslims who have the means to make the journey to Mecca.

Iran banned all pilgrimages to Saudi Arabia during Ramadan in an attempt to contain the spread of the virus.